diff --git a/data/day12/example01.txt b/data/day12/example01.txt
new file mode 100644
index 0000000..433e0d2
--- /dev/null
+++ b/data/day12/example01.txt
@@ -0,0 +1,5 @@
+Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi
\ No newline at end of file
diff --git a/data/day12/input.txt b/data/day12/input.txt
new file mode 100644
index 0000000..b226042
--- /dev/null
+++ b/data/day12/input.txt
@@ -0,0 +1,41 @@
+abcccaaaaaaccccccccaaaaaccccccaaaaaaccccccaaaaaaaacccaaaaaaaccaaaacccccccccccccccccccccccccaaaaaacccccccccccccccccccccccccccccaaaaaa
+abcccaaaaaacccccccaaaaaaccccaaaaaaaacccccccaaaaaaaaaaaaaaaaccaaaaacccccccccccccccccccccccccaaaaaacccccccccccccccccccccccccccccaaaaaa
+abccccaaaaacaaaccaaaaaaaacccaaaaaaaaacccccccaaaaaaaaaaaaaaaacaaaaaacccccccccaaacccccccccccaaaaaaaaccccccccccaaccccccccccccccccaaaaaa
+abccccaaaaccaaaaaaaaaaaaacccaaaaaaaaaacccccaaaaaaaaaaaaaaaaaaacaaaacccccccccaaaacccccccccaaaaaaaaaacccccccccaaaccccccccccccccccccaaa
+abcccccccccaaaaaacccaacccccccccaaacaaaccccccaacccccccaaaaaaaaacaacccccccccccaaaacccccccccaaaaaaaaaacccccccccaaaccacaaccccccccccccaaa
+abcccccccccaaaaaacccaacccccccccaaacccccccccccccccccccaaaacaaaacccccccaacaaccaaaccccccccccaccaaaaacacccccccccaaaacaaaaccccccccccccaac
+abccccccccccaaaaacccccccccccccccacccaaaacccccccccccccaaaacccccccccccccaaaacccccccccccaacccccaaaaccccccccjjjjaaaaaaaaaccccccccccccccc
+abccccccccccaaaacccccccccccccccccccaaaaacccccccccccccaaaccccccccccccccaaaaacccccccccaaaaaacccaaccccccccjjjjjjkkaaaacccccccccaacccccc
+abcccccaaccccccccccccccccccccccccccaaaaaacccccccccccccaacccccccccccccaaaaaaccccccccccaaaaaccccccccccccjjjjjjjkkkkaacccccaacaaacccccc
+abccaaaacccccccccccccccccccccccccccaaaaaaccccccccccccccccccccccccccccaaaacaccccccccaaaaaaaccccaacccccjjjjoooookkkkkkkklllaaaaaaacccc
+abccaaaaaacccccccccccccccccccccccccaaaaacccccccccccccccccccccccccccccccaaccccccccccaaaaaaaaccaaaaccccjjjoooooookkkkkkkllllaaaaaacccc
+abcccaaaaacccccccccccccccccccccccccccaaaccccccccaaaacccccccccccccccccccccccccccccccaaaaaaaaccaaaaccccjjooooooooppkkppplllllaccaacccc
+abccaaaaaccccccccccccaccccccccccccccccccccccccccaaaacccccccccccccccccccccccccccccccccaaacacccaaaacccijjooouuuuoppppppppplllccccccccc
+abcccccaacccccccccccaaaaaaaaccccccccccccccccccccaaaaccccaaccccccccaaacccccccccccccaacaaccccccccccccciijoouuuuuuppppppppplllcccaccccc
+abcccccccccccccccccccaaaaaaccccccccccccccccccccccaaccccaaaacccccccaaaaccccccccccaaaaaaccccccccccccciiiiootuuuuuupuuuvvpppllccccccccc
+abcccccccccccccccccccaaaaaaccaaaaacccccccccccccccccccccaaaacccccccaaaaccccccccccaaaaaaccccccccccccciiinnotuuxxxuuuuvvvpppllccccccccc
+abccccccccccccccacccaaaaaaaacaaaaaaacccccccccccccccccccaaaacccccccaaacccccaaaaccaaaaaccccaaccccccciiiinnnttxxxxuuyyyvvqqqllccccccccc
+abcccccccccccaaaaccaaaaaaaaaaaaaaaaaaccaacccccccccccccccccccccccccccccccccaaaacccaaaaaccaaacccccciiinnnnnttxxxxxyyyyvvqqqllccccccccc
+abaaaacccccccaaaaaaaaaaaaaaaaaaaaaaaaaaaacccccccccccccccccccccccccccccccccaaaacccaaaaaacaaaccccciiinnnnttttxxxxxyyyyvvqqmmmccccccccc
+abaaaaccccccccaaaaacccaaaaacaaaaaacaaaaaaccccccccccccccccaaccccccccccccccccaacccccccaaaaaaaaaaciiinnnnttttxxxxxyyyyvvqqqmmmccccccccc
+SbaaaacccccccaaaaaccccaaaaaccaaaaaaaaaaaccccccccccccccccaaacaacccccccccccccccccccccccaaaaaaaaachhhnnntttxxxEzzzzyyvvvqqqmmmccccccccc
+abaaaacccccccaacaacccccaaaaaaaacaaaaaaaaaccccccccccccccccaaaaaccccccccccccccccccccccccaaaaaaacchhhnnntttxxxxxyyyyyyvvvqqmmmdddcccccc
+abaaaacccccccccccccccccccaaaaaacaaaaaaaaaacccccccccccccaaaaaaccccccccaaaccccccccccccccaaaaaaccchhhnnntttxxxxywyyyyyyvvvqqmmmdddccccc
+abaacccccccccccccccccccaaaaaaacccccaaaaaaacccccccccccccaaaaaaaacccccaaaacccccccccccccaaaaaaacaahhhmmmttttxxwwyyyyyyyvvvqqmmmdddccccc
+abcccccccccccccccccccccaaaaaaacaaccaaacccccccccccccccccaacaaaaacccccaaaacccccccccccccaaacaaaaaahhhmmmmtsssswwyywwwwvvvvqqqmmdddccccc
+abcccccccccccccccaaaccccaaaaaaaaaacaaccaaccccccccccccccccaaacaccccccaaaacccccccccccccccccaaaaacahhhmmmmmsssswwywwwwwvvrrqqmmdddccccc
+abcccccccccccccaaaaaaccccaaaaaaaaaccaaaacccccccccccccccccaacccccccccccccccccccccccaaaccccaaaaaaahhhhhmmmmssswwwwwrrrrrrrrmmmmddccccc
+abcccccccccccccaaaaaaccccaaaaaaaaaaaaaaaaaccccccccccccccccccccccccccccccccccccccaaaaaacccccaaaaachhhhhmmmmsswwwwrrrrrrrrrkkmdddccccc
+abccccccccccccccaaaaaccccccaaaaaaaaaaaaaaaccccccccccccccccccccccccccccccccccccccaaaaaaccccaaaaacccchhggmmmssswwrrrrrkkkkkkkkdddacccc
+abccaaaacccccccaaaaacccccccccaaaaaacaaaaacccccccccccccccccccccccccccccccccccccccaaaaaaccccaacaaaccccggggmmsssssrrlkkkkkkkkkdddaccccc
+abccaaaacccccccaaaaacccccccccaaaaaaccccaacccccccccccccccccccccccccccccccccccccccaaaaaccccccccaaccccccgggmllssssrllkkkkkkkeeeddaccccc
+abccaaaacccccccaaacccccccccccaaaaaacccccccccccccccccccaacccccccccccccccccccccccaaaaaacccccccccccccccccggllllssslllkkeeeeeeeeeaaacccc
+abcccaaccccccccaaacaaaccccccaaaaaaaaaaacccccccccccccaaaaaacccccccccccccccccccccaaacaaacccccaacccccccccggglllllllllfeeeeeeeeaaaaacccc
+abccccccccccaaaaaaaaaaccccccccccccaccaaaccacccccccccaaaaaaccccaaccaacccaaccccccaaaaaaacccccaaccccccccccggglllllllfffeeecccaaaaaacccc
+abccccccccccaaaaaaaaacccccccccccccccaaaaaaaccccccccccaaaaaccccaaaaaacccaaaaaaccaaaaaacccaaaaaaaacccccccggggllllfffffccccccaacccccccc
+abcccccccccccaaaaaaacccccccccccccccccaaaaaaccaacccccaaaaaccccccaaaaacccaaaaaacaaaaaaacccaaaaaaaaccccccccgggffffffffccccccccccccccccc
+abccccccccccccaaaaaaacccccccccccccaaaaaaaaacaaaaccccaaaaacaaaaaaaaaacaaaaaaacaaaaaaaaaccccaaaacccccccccccggffffffacccccccccccccccaaa
+abccccccccccccaaaaaaacaaccccccccccaaaaaaaaacaaaacccccaaaaaaaaaaaaaaaaaaaaaaacaaaaaaaaaacccaaaaacccccccccccaffffaaaaccccccccccccccaaa
+abccccccccccccaaacaaaaaacccccccccccaaaaaaaacaaaaaaaaaaaaaaaaaaaaaaaaacaaaaaaacccaaacaaaccaaaaaacccccccccccccccccaaaccccccccccccccaaa
+abccccccccccccaaccaaaaaccccccccccccccaaaaaaaccccaaaaaaaaaaaaccccaacccccaaaaaacccaaaccccccaaccaacccccccccccccccccaaacccccccccccaaaaaa
+abcccccccccccccccaaaaaaaaccccccccccccaacccacccccccaaaaaaaaaaccccaacccccaaccccccccaccccccccccccccccccccccccccccccccccccccccccccaaaaaa
\ No newline at end of file
diff --git a/src/days/day12/mod.rs b/src/days/day12/mod.rs
new file mode 100644
index 0000000..c3f6ab1
--- /dev/null
+++ b/src/days/day12/mod.rs
@@ -0,0 +1,294 @@
+use std::collections::{BinaryHeap, HashSet};
+
+use crate::common::pos::Pos;
+
+use super::template::{DayTrait, ResultType};
+use thiserror::Error;
+
+const DAY_NUMBER: usize = 12;
+
+pub struct Day;
+
+impl DayTrait for Day {
+    fn get_day_number(&self) -> usize {
+        DAY_NUMBER
+    }
+
+    fn part1(&self, lines: &[String]) -> anyhow::Result<ResultType> {
+        let valley = Valley::parse(lines)?;
+        Ok(ResultType::Integer(valley.walk()? as i64))
+    }
+
+    fn part2(&self, lines: &[String]) -> anyhow::Result<ResultType> {
+        let valley = Valley::parse(lines)?;
+        Ok(ResultType::Integer(valley.walk_short()? as i64))
+    }
+}
+
+#[derive(Debug, Error)]
+enum ValleyError {
+    #[error("Not a legal terrain char: {0}")]
+    NotALegalCharacter(char),
+    #[error("Valley needs to be rectangle")]
+    NotAReactangleValley,
+    #[error("Valley map conatins no data")]
+    EmptyValley,
+    #[error("Could not find start point")]
+    NoStartFound,
+    #[error("Could not find exit point")]
+    NoExitFound,
+    #[error("No path found")]
+    NoPathFound,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+struct Path {
+    length: usize,
+    height: char,
+    pos: Pos<usize>,
+}
+
+impl PartialOrd for Path {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        match other.length.partial_cmp(&self.length) {
+            Some(core::cmp::Ordering::Equal) => {}
+            ord => return ord,
+        }
+        match other.height.partial_cmp(&self.height) {
+            Some(core::cmp::Ordering::Equal) => {}
+            ord => return ord,
+        }
+        match self.pos.x().partial_cmp(&other.pos.x()) {
+            Some(core::cmp::Ordering::Equal) => {}
+            ord => return ord,
+        }
+        self.pos.y().partial_cmp(&other.pos.y())
+    }
+}
+
+impl Ord for Path {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        other
+            .length
+            .cmp(&self.length)
+            .then_with(|| other.height.cmp(&self.height))
+            .then_with(|| self.pos.x().cmp(&other.pos.x()))
+            .then_with(|| self.pos.y().cmp(&other.pos.y()))
+    }
+}
+
+impl Path {
+    pub fn new(length: usize, height: char, pos: Pos<usize>) -> Self {
+        Path {
+            length,
+            height,
+            pos,
+        }
+    }
+
+    pub fn next_path<'a>(&'a self, valley: &'a Valley) -> Neighbors<'a> {
+        Neighbors::new(self, valley)
+    }
+}
+
+struct Neighbors<'a> {
+    path: &'a Path,
+    valley: &'a Valley,
+    state: usize,
+}
+
+impl<'a> Neighbors<'a> {
+    pub fn new(path: &'a Path, valley: &'a Valley) -> Self {
+        Neighbors {
+            path,
+            state: 0,
+            valley,
+        }
+    }
+
+    fn next_pos(&mut self) -> Option<Pos<usize>> {
+        while self.state < 4 {
+            self.state += 1;
+            match self.state {
+                1 => {
+                    if self.path.pos.x() < self.valley.width() - 1 {
+                        return Some(Pos::new(self.path.pos.x() + 1, self.path.pos.y()));
+                    }
+                }
+                2 => {
+                    if self.path.pos.y() > 0 {
+                        return Some(Pos::new(self.path.pos.x(), self.path.pos.y() - 1));
+                    }
+                }
+                3 => {
+                    if self.path.pos.x() > 0 {
+                        return Some(Pos::new(self.path.pos.x() - 1, self.path.pos.y()));
+                    }
+                }
+                4 => {
+                    if self.path.pos.y() < self.valley.height() - 1 {
+                        return Some(Pos::new(self.path.pos.x(), self.path.pos.y() + 1));
+                    }
+                }
+                _ => {}
+            }
+        }
+        None
+    }
+}
+
+impl Iterator for Neighbors<'_> {
+    type Item = Path;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(pos) = self.next_pos() {
+            let height = self.valley.get_height(pos);
+            if height as u32 + 1 >= self.path.height as u32 {
+                return Some(Path::new(self.path.length + 1, height, pos));
+            }
+        }
+        None
+    }
+}
+
+struct Valley {
+    map: Vec<Vec<char>>,
+    start: Pos<usize>,
+    exit: Pos<usize>,
+    width: usize,
+}
+
+impl Valley {
+    pub fn parse(lines: &[String]) -> Result<Valley, ValleyError> {
+        let mut map = Vec::new();
+        let mut start = None;
+        let mut exit = None;
+        let mut valley_width = None;
+        for (y, row) in lines.iter().enumerate() {
+            let mut height_row = Vec::new();
+            for (x, height_char) in row.chars().enumerate() {
+                match height_char {
+                    'S' => {
+                        start = Some(Pos::new(x, y));
+                        height_row.push('a')
+                    }
+                    'E' => {
+                        exit = Some(Pos::new(x, y));
+                        height_row.push('z')
+                    }
+                    'a'..='z' => height_row.push(height_char),
+                    _ => return Err(ValleyError::NotALegalCharacter(height_char)),
+                }
+            }
+            if let Some(width) = valley_width {
+                if width != height_row.len() {
+                    return Err(ValleyError::NotAReactangleValley);
+                }
+            } else {
+                valley_width = Some(height_row.len());
+            }
+            map.push(height_row);
+        }
+        let Some(width) = valley_width else {
+            return Err(ValleyError::EmptyValley);
+        };
+        let Some(start) = start else {
+            return Err(ValleyError::NoStartFound);
+        };
+        let Some(exit) = exit else {
+            return Err(ValleyError::NoExitFound);
+        };
+        Ok(Valley {
+            map,
+            start,
+            exit,
+            width,
+        })
+    }
+
+    fn get_height(&self, pos: Pos<usize>) -> char {
+        self.map[pos.y()][pos.x()]
+    }
+
+    fn do_walk<F>(&self, check: F) -> Result<usize, ValleyError>
+    where
+        F: Fn(Pos<usize>) -> bool,
+    {
+        let mut shortest = HashSet::with_capacity(self.width * self.map.len());
+        let mut queue = BinaryHeap::new();
+        queue.push(Path::new(0, 'z', self.exit));
+        while let Some(current) = queue.pop() {
+            if check(current.pos) {
+                return Ok(current.length);
+            }
+            if shortest.contains(&current.pos) {
+                continue;
+            }
+            shortest.insert(current.pos);
+            for next in current.next_path(self) {
+                queue.push(next);
+            }
+        }
+
+        Err(ValleyError::NoPathFound)
+    }
+
+    pub fn walk(&self) -> Result<usize, ValleyError> {
+        self.do_walk(|pos| pos == self.start)
+    }
+
+    pub fn walk_short(&self) -> Result<usize, ValleyError> {
+        self.do_walk(|pos| self.get_height(pos) == 'a')
+    }
+
+    #[inline]
+    fn width(&self) -> usize {
+        self.width
+    }
+
+    #[inline]
+    fn height(&self) -> usize {
+        self.map.len()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::common::file::read_lines;
+    use anyhow::Result;
+
+    #[test]
+    fn test_parse() -> Result<()> {
+        let day = Day {};
+        let lines = read_lines(day.get_day_number(), "example01.txt")?;
+        let valley = Valley::parse(&lines)?;
+        assert_eq!(valley.width, 8);
+        assert_eq!(valley.start, Pos::new(0, 0));
+        assert_eq!(valley.exit, Pos::new(5, 2));
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let day = Day {};
+        let lines = read_lines(day.get_day_number(), "example01.txt")?;
+        let expected = ResultType::Integer(31);
+        let result = day.part1(&lines)?;
+        assert_eq!(result, expected);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_part2() -> Result<()> {
+        let day = Day {};
+        let lines = read_lines(day.get_day_number(), "example01.txt")?;
+        let expected = ResultType::Integer(29);
+        let result = day.part2(&lines)?;
+        assert_eq!(result, expected);
+
+        Ok(())
+    }
+}
diff --git a/src/days/mod.rs b/src/days/mod.rs
index 7cd8179..0602f75 100644
--- a/src/days/mod.rs
+++ b/src/days/mod.rs
@@ -9,6 +9,7 @@ mod day08;
 mod day09;
 mod day10;
 mod day11;
+mod day12;
 mod template;
 
 pub use template::DayTrait;
@@ -18,7 +19,7 @@ pub mod day_provider {
     use super::*;
     use thiserror::Error;
 
-    const MAX_DAY: usize = 11;
+    const MAX_DAY: usize = 12;
 
     pub fn get_day(day_num: usize) -> Result<Box<dyn DayTrait>, ProviderError> {
         match day_num {
@@ -33,6 +34,7 @@ pub mod day_provider {
             9 => Ok(Box::new(day09::Day)),
             10 => Ok(Box::new(day10::Day)),
             11 => Ok(Box::new(day11::Day)),
+            12 => Ok(Box::new(day12::Day)),
             _ => Err(ProviderError::InvalidNumber(day_num)),
         }
     }