diff --git a/src/cell.rs b/src/cell.rs
new file mode 100644
index 0000000..4b185e8
--- /dev/null
+++ b/src/cell.rs
@@ -0,0 +1,20 @@
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum CellType {
+    Empty = 0,
+    Sand,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum MovementType {
+    None = 0b0000_0000,
+    Down = 0b0000_0001,
+    Side = 0b0000_0010,
+    DownSide = 0b0000_0011,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Cell {
+    pub cell_type: CellType,
+    pub movement_type: MovementType,
+    pub color: u32,
+}
diff --git a/src/engine.rs b/src/engine.rs
index 8135807..8a50411 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -5,13 +5,15 @@ use minifb::{Key, Window, WindowOptions};
 const WIDTH: usize = 800;
 const HEIGHT: usize = 600;
 
-use crate::{materials::*, rand::Random};
+use crate::{materials::*, rand::Random, world::World};
 
 pub struct Engine {
     pub window: Window,
-    pub buffer: Vec<u32>,
+    pub front_buffer: Vec<u32>,
     pub brush_size: usize,
     pub random: Random,
+
+    pub world: World,
 }
 
 impl Engine {
@@ -26,9 +28,10 @@ impl Engine {
             .unwrap_or_else(|e| {
                 panic!("{}", e);
             }),
-            buffer: vec![0; WIDTH * HEIGHT],
+            front_buffer: vec![0; WIDTH * HEIGHT],
             brush_size: 1,
             random: Random::new(0),
+            world: World::new(),
         }
     }
 
@@ -83,19 +86,13 @@ impl Engine {
             for x in 0..WIDTH {
                 for y in 0..HEIGHT {
                     let index = xy_to_i(x, y);
-                    let cell = self.buffer[index];
+                    let cell = self.front_buffer[index];
 
                     if cell == SAND {
                         let down = self.is_empty(x, y + 1);
-                        let mut left = self.is_empty(x - 1, y + 1);
-                        let mut right = self.is_empty(x + 1, y + 1);
-
-                        if left && right {
-                            // TODO: handle left/right randomization here
-                            let rand = self.random.random_bool();
-                            left = rand;
-                            right = !rand;
-                        }
+                        let random = self.random.random_bool();
+                        let left = self.is_empty(x - 1, y + 1) && random;
+                        let right = self.is_empty(x + 1, y + 1) ^ left;
 
                         if down {
                             self.set_cell(x, y + 1, SAND)
@@ -113,7 +110,7 @@ impl Engine {
             }
             // TODO Handle this.
             self.window
-                .update_with_buffer(&self.buffer, WIDTH, HEIGHT)
+                .update_with_buffer(&self.front_buffer, WIDTH, HEIGHT)
                 .unwrap();
         }
     }
@@ -122,18 +119,18 @@ impl Engine {
 impl Engine {
     fn is_empty(&mut self, x: usize, y: usize) -> bool {
         let index = xy_to_i(x, y);
-        if index >= self.buffer.len() {
+        if index >= self.front_buffer.len() {
             false
         } else {
-            self.buffer[index] == EMPTY
+            self.front_buffer[index] == EMPTY
         }
     }
 
     fn set_cell(&mut self, x: usize, y: usize, mat: u32) {
         let index = xy_to_i(x, y);
-        if index >= self.buffer.len() {
+        if index >= self.front_buffer.len() {
         } else {
-            self.buffer[index] = mat;
+            self.front_buffer[index] = mat;
         }
     }
 
@@ -141,7 +138,7 @@ impl Engine {
         for x in 0..WIDTH {
             for y in 0..HEIGHT {
                 let index = xy_to_i(x, y);
-                self.buffer[index] = EMPTY;
+                self.front_buffer[index] = EMPTY;
             }
         }
     }
diff --git a/src/main.rs b/src/main.rs
index e29f2f7..7455dcf 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,8 @@
+mod cell;
 mod engine;
 mod materials;
 mod rand;
+mod world;
 
 fn main() {
     let mut engine = engine::Engine::new();
diff --git a/src/world.rs b/src/world.rs
new file mode 100644
index 0000000..c38648e
--- /dev/null
+++ b/src/world.rs
@@ -0,0 +1,57 @@
+use crate::cell::{Cell, MovementType};
+
+use crate::cell::CellType::Empty;
+use crate::engine::xy_to_i;
+use crate::materials::EMPTY;
+
+const WIDTH: usize = 800;
+const HEIGHT: usize = 600;
+
+pub struct World {
+    pub width: usize,
+    pub height: usize,
+    pub cells: Vec<Cell>,
+}
+impl World {
+    pub fn new() -> Self {
+        Self {
+            width: WIDTH,
+            height: HEIGHT,
+            cells: vec![
+                Cell {
+                    cell_type: Empty,
+                    movement_type: MovementType::None,
+                    color: 0
+                };
+                WIDTH * HEIGHT
+            ],
+        }
+    }
+}
+
+impl World {
+    pub fn get_xy(&mut self, x: usize, y: usize) -> Cell {
+        let index = x + self.width * y;
+
+        self.cells[index]
+    }
+
+    pub fn get_i(&mut self, index: usize) -> Cell {
+        self.cells[index]
+    }
+
+    pub fn is_empty(&mut self, x: usize, y: usize) -> bool {
+        in_bounds(x, y) && self.get_xy(x, y).cell_type == Empty
+    }
+
+    pub fn set_xy(&mut self, x: usize, y: usize, cell: Cell) {
+        self.cells[xy_to_i(x, y)] = cell
+    }
+}
+
+pub fn in_bounds(x: usize, y: usize) -> bool {
+    let x_in_bounds = x < WIDTH;
+    let y_in_bounds = y < HEIGHT;
+
+    x_in_bounds && y_in_bounds
+}