diff --git a/src/exit.rs b/src/exit.rs
index 5ed5b6d..4d7b2c4 100644
--- a/src/exit.rs
+++ b/src/exit.rs
@@ -1,4 +1,4 @@
-use crate::Position;
+use crate::{Position, from_base36, to_base36};
 
 #[derive(Debug, Eq, PartialEq)]
 pub enum Transition {
@@ -48,7 +48,7 @@ impl ToString for Transition {
 #[derive(Debug, Eq, PartialEq)]
 pub struct Exit {
     /// destination
-    pub room: String,  /// id
+    pub room_id: u64,  /// id
     pub position: Position,
     pub effect: Transition,
 }
@@ -57,7 +57,7 @@ impl From<String> for Exit {
     fn from(string: String) -> Exit {
         // e.g. "EXT 6,4 0 10,12 FX fade_w"
         let room_position_effect: Vec<&str> = string.split_whitespace().collect();
-        let room = room_position_effect[0].to_string();
+        let room_id = from_base36(room_position_effect[0]);
         let position = Position::from(room_position_effect[1].to_string());
 
         let effect = if room_position_effect.len() == 4 {
@@ -66,13 +66,18 @@ impl From<String> for Exit {
             Transition::None
         };
 
-        Exit { room, position, effect }
+        Exit { room_id, position, effect }
     }
 }
 
 impl ToString for Exit {
     fn to_string(&self) -> String {
-        format!("{} {}{}", self.room, self.position.to_string(), self.effect.to_string())
+        format!(
+            "{} {}{}",
+            to_base36(self.room_id),
+            self.position.to_string(),
+            self.effect.to_string()
+        )
     }
 }
 
@@ -80,7 +85,7 @@ impl ToString for Exit {
 fn test_exit_from_string() {
     assert_eq!(
         Exit::from("a 12,13".to_string()),
-        Exit { room: "a".to_string(), position: Position { x: 12, y: 13 }, effect: Transition::None }
+        Exit { room_id: 10, position: Position { x: 12, y: 13 }, effect: Transition::None }
     );
 }
 
@@ -88,18 +93,14 @@ fn test_exit_from_string() {
 fn test_exit_from_string_with_fx() {
     assert_eq!(
         Exit::from("a 12,13 FX slide_u".to_string()),
-        Exit { room: "a".to_string(), position: Position { x: 12, y: 13 }, effect: Transition::SlideUp }
+        Exit { room_id: 10, position: Position { x: 12, y: 13 }, effect: Transition::SlideUp }
     );
 }
 
 #[test]
 fn test_exit_to_string() {
     assert_eq!(
-        Exit {
-            room: "8".to_string(),
-            position: Position { x: 5, y: 6 },
-            effect: Transition::None
-        }.to_string(),
+        Exit { room_id: 8, position: Position { x: 5, y: 6 }, effect: Transition::None}.to_string(),
         "8 5,6".to_string()
     );
 }
@@ -108,7 +109,7 @@ fn test_exit_to_string() {
 fn test_exit_to_string_with_fx() {
     assert_eq!(
         Exit {
-            room: "8".to_string(),
+            room_id: 8,
             position: Position { x: 5, y: 6 },
             effect: Transition::FadeToWhite
         }.to_string(),
diff --git a/src/mock.rs b/src/mock.rs
index cb44fa0..ef356e1 100644
--- a/src/mock.rs
+++ b/src/mock.rs
@@ -149,7 +149,11 @@ pub fn room() -> Room {
         exits: vec![
             ExitInstance {
                 position: Position { x: 3, y: 3},
-                exit: Exit { room: "3".to_string(), position: Position { x: 10, y: 6}, effect: Transition::None}
+                exit: Exit {
+                    room_id: 3,
+                    position: Position { x: 10, y: 6},
+                    effect: Transition::None
+                }
             },
         ],
         endings: vec![