diff --git a/src/day15.rs b/src/day15.rs
new file mode 100644
index 0000000..5aa1f3b
--- /dev/null
+++ b/src/day15.rs
@@ -0,0 +1,172 @@
+use crate::util::maps::*;
+use itertools::Itertools;
+use pest::{
+    iterators::{Pair, Pairs},
+    Parser,
+};
+use pest_derive::Parser;
+use std::fmt::Display;
+
+const DOUBLE_WIDE: bool = true;
+
+pub fn day15() {
+    let (mut map, directions) = parse(&crate::input(15));
+    if DOUBLE_WIDE {
+        map = double_wide_map(map);
+    }
+
+    let (mut x, mut y, _) = map
+        .enumerate()
+        .find(|(_, _, &t)| t == Terrain::Robot)
+        .unwrap();
+
+    for direction in directions {
+        if let Some(new_map) = move_on_map(&map, x, y, direction) {
+            map = new_map;
+            (x, y) = map.travel(x, y, direction).unwrap();
+        }
+    }
+
+    let sum_gps: usize = map
+        .enumerate()
+        .filter(|(_, _, &t)| {
+            t == Terrain::Block(None) || t == Terrain::Block(Some(Direction::East))
+        })
+        .map(|(x, y, _)| y * 100 + x)
+        .sum();
+
+    println!("{}", map);
+    println!("Sum of GPS Coordinates: {}", sum_gps);
+}
+
+fn move_on_map(
+    map: &Map<Terrain>,
+    x: usize,
+    y: usize,
+    direction: Direction,
+) -> Option<Map<Terrain>> {
+    let cascading_move = || {
+        let (nx, ny) = map.travel(x, y, direction)?;
+        let mut downstream = move_on_map(map, nx, ny, direction)?;
+        downstream.set(nx, ny, map.get(x, y).unwrap());
+        downstream.set(x, y, Terrain::Empty);
+        Some(downstream)
+    };
+
+    match map.get(x, y).unwrap() {
+        Terrain::Wall => None,
+        Terrain::Empty => Some(map.clone()),
+        Terrain::Block(None) => (cascading_move)(),
+        Terrain::Block(Some(d)) if d.is_parallel(direction) => (cascading_move)(),
+        Terrain::Robot => (cascading_move)(),
+        Terrain::Block(Some(Direction::West)) => {
+            let (partner_x, partner_y) = map.travel(x, y, Direction::West).unwrap();
+            move_on_map(map, partner_x, partner_y, direction)
+        }
+        Terrain::Block(Some(Direction::East)) => {
+            let (partner_x, partner_y) = map.travel(x, y, Direction::East).unwrap();
+
+            let mut downstream = (cascading_move)()?;
+            let (partner_nx, partner_ny) = map.travel(partner_x, partner_y, direction).unwrap();
+            downstream = move_on_map(&downstream, partner_nx, partner_ny, direction)?;
+            downstream.set(
+                partner_nx,
+                partner_ny,
+                map.get(partner_x, partner_y).unwrap(),
+            );
+            downstream.set(partner_x, partner_y, Terrain::Empty);
+
+            Some(downstream)
+        }
+        Terrain::Block(Some(_)) => unimplemented!("North/South blocks are not implemented."),
+    }
+}
+
+fn double_wide_map(map: Map<Terrain>) -> Map<Terrain> {
+    let new_map = map
+        .iter_rows()
+        .map(|row| {
+            row.iter()
+                .flat_map(|&t| match t {
+                    Terrain::Wall => vec![Terrain::Wall; 2],
+                    Terrain::Empty => vec![Terrain::Empty; 2],
+                    Terrain::Block(None) => vec![
+                        Terrain::Block(Some(Direction::East)),
+                        Terrain::Block(Some(Direction::West)),
+                    ],
+                    Terrain::Robot => vec![Terrain::Robot, Terrain::Empty],
+                    Terrain::Block(Some(_)) => unreachable!(),
+                })
+                .collect()
+        })
+        .collect();
+    Map::from_2d_vec(new_map)
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+enum Terrain {
+    Wall,
+    Empty,
+    Block(Option<Direction>),
+    Robot,
+}
+
+impl Display for Terrain {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let s = match self {
+            Terrain::Robot => "@",
+            Terrain::Wall => "#",
+            Terrain::Empty => ".",
+            Terrain::Block(Some(Direction::East)) => "[",
+            Terrain::Block(Some(Direction::West)) => "]",
+            Terrain::Block(_) => "O",
+        };
+        f.write_str(s)
+    }
+}
+
+#[derive(Parser)]
+#[grammar = "grammars/day15.pest"]
+struct Day15Parser {}
+
+fn parse(input: &str) -> (Map<Terrain>, Vec<Direction>) {
+    let (map, directions) = Day15Parser::parse(Rule::input, input)
+        .unwrap()
+        .nth(0)
+        .unwrap()
+        .into_inner()
+        .map(Pair::<'_, Rule>::into_inner)
+        .collect_tuple()
+        .unwrap();
+
+    (parse_map(map), parse_directions(directions))
+}
+
+fn parse_map(input: Pairs<'_, Rule>) -> Map<Terrain> {
+    let map_vec = input
+        .map(Pair::<'_, Rule>::into_inner)
+        .map(|row| {
+            row.map(|terrain| match terrain.as_rule() {
+                Rule::wall => Terrain::Wall,
+                Rule::empty => Terrain::Empty,
+                Rule::block => Terrain::Block(None),
+                Rule::robot => Terrain::Robot,
+                _ => unreachable!(),
+            })
+            .collect()
+        })
+        .collect();
+    Map::from_2d_vec(map_vec)
+}
+
+fn parse_directions(input: Pairs<'_, Rule>) -> Vec<Direction> {
+    input
+        .map(|d| match d.as_rule() {
+            Rule::north => Direction::North,
+            Rule::west => Direction::West,
+            Rule::east => Direction::East,
+            Rule::south => Direction::South,
+            _ => unreachable!(),
+        })
+        .collect()
+}
diff --git a/src/grammars/day15.pest b/src/grammars/day15.pest
new file mode 100644
index 0000000..cf94863
--- /dev/null
+++ b/src/grammars/day15.pest
@@ -0,0 +1,19 @@
+_WHITESPACE = _{ " " }
+NEWLINE = _{ "\n" }
+
+wall = @{ "#" }
+empty = @{ "." }
+block = @{ "O" }
+robot = @{ "@" }
+space = _{ wall | empty | block | robot }
+row = { space+ ~ NEWLINE+ }
+map = { row+ }
+
+north = @{ "^" }
+west = @{ "<" }
+east = @{ ">" }
+south = @{ "v" }
+direction_list = { ((north | west | east | south) ~ NEWLINE*)+ }
+
+eoi = _{ !ANY }
+input = { SOI ~ map ~ direction_list ~ eoi }
diff --git a/src/main.rs b/src/main.rs
index 4d70f0f..8f686d5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -26,10 +26,12 @@ mod day11;
 mod day12;
 #[allow(dead_code)]
 mod day13;
+#[allow(dead_code)]
 mod day14;
+mod day15;
 
 fn main() {
-    day14::day14();
+    day15::day15();
 }
 
 pub fn input(day: u8) -> String {
diff --git a/src/util/maps.rs b/src/util/maps.rs
index 55072f8..88b21ff 100644
--- a/src/util/maps.rs
+++ b/src/util/maps.rs
@@ -1,6 +1,8 @@
+use std::fmt::Display;
+
 use itertools::Itertools;
 
-#[derive(Copy, Clone, PartialEq, Eq)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum Direction {
     North,
     South,
@@ -12,12 +14,25 @@ impl Direction {
     pub fn all_variants() -> Vec<Self> {
         vec![Self::North, Self::East, Self::West, Self::South]
     }
+
+    pub fn opposite(self) -> Self {
+        match self {
+            Self::North => Self::South,
+            Self::East => Self::West,
+            Self::West => Self::East,
+            Self::South => Self::North,
+        }
+    }
+
+    pub fn is_parallel(self, other: Self) -> bool {
+        self == other || self == other.opposite()
+    }
 }
 
 #[derive(Clone)]
 pub struct Map<T>
 where
-    T: Copy,
+    T: Copy + Display,
 {
     pub map: Vec<Vec<T>>,
 }
@@ -36,7 +51,7 @@ impl Map<char> {
 
 impl<T> Map<T>
 where
-    T: Copy,
+    T: Copy + Display,
 {
     pub fn from_2d_vec(map: Vec<Vec<T>>) -> Self {
         Self { map }
@@ -69,13 +84,23 @@ where
         }
     }
 
+    pub fn get(&self, x: usize, y: usize) -> Option<T> {
+        Some(*self.map.get(y)?.get(x)?)
+    }
+
     pub fn travel_get(&self, x: usize, y: usize, direction: Direction) -> Option<T> {
         let (nx, ny) = self.travel(x, y, direction)?;
         self.get(nx, ny)
     }
 
-    pub fn get(&self, x: usize, y: usize) -> Option<T> {
-        Some(*self.map.get(y)?.get(x)?)
+    pub fn travel_and_get(
+        &self,
+        x: usize,
+        y: usize,
+        direction: Direction,
+    ) -> Option<(usize, usize, T)> {
+        let (nx, ny) = self.travel(x, y, direction)?;
+        Some((nx, ny, self.get(nx, ny)?))
     }
 
     pub fn set(&mut self, x: usize, y: usize, value: T) {
@@ -98,6 +123,10 @@ where
         self.map.iter().flat_map(|row| row.iter())
     }
 
+    pub fn iter_rows(&self) -> impl Iterator<Item = &Vec<T>> {
+        self.map.iter()
+    }
+
     pub fn coordinates(&self) -> impl Iterator<Item = (usize, usize)> {
         (0..self.width()).cartesian_product(0..self.height())
     }
@@ -106,3 +135,21 @@ where
         self.coordinates().map(|(x, y)| (x, y, &self.map[y][x]))
     }
 }
+
+impl<T> Display for Map<T>
+where
+    T: Copy + Display,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut final_string = "".to_string();
+        for row in self.map.iter() {
+            let s = row.iter().fold("".to_string(), |mut acc, e| {
+                acc.push_str(&format!("{}", e));
+                acc
+            });
+            final_string.push_str("\n");
+            final_string.push_str(&s);
+        }
+        f.write_str(&final_string)
+    }
+}