Crawl Space

Crawl Spaces (also known as Retro Treasure Rooms) are small secret rooms which can be entered by touching trapdoors with ladders in them. They can be found in 5 different ways:

1. Using the We Need to Go Deeper! activated item (10% chance)
2. Using the Ehwaz rune (8% chance)
3. Bombing a Clean Bedroom rug (100% chance)
4. Bombing a Dirty Bedroom rug (unknown chance)
5. Destroying a rock (unknown very small chance)

Crawl Spaces only have one layout: They consist of 2 ladders and an Item, Chest, Trinket, or various pickups. These rooms are viewed from the side, rather than from above like the rest of the game, and Isaac will experience gravity pulling him to the floor while he is not walking on top of one of the ladders. Under the effects of flight, this gravity has no effect. However, Isaac cannot fly over the walls or floor.

Mechanics

When entering a room pre-determined to contain a Crawl Space entrance, a RNG roll is made using the floor seed. This value will be shifted and divided, until its final result is in the grid range for the current room (ie: 128 tiles for 1x1 rooms, or 16x8). If said tile value is tied to a simple rock (not tinted, not a prop), then an access to the Crawl Space will be granted upon destroying that rock. Only one room per floor has the right to spawn a Crawl Space, and not every floor is given one during the initial generation, even though every floor has also a Crawl Space and a Black Market ready in queue. The tile value can also be tied to props (empty tiles, doors, pots, void tiles, spikes, metal blocks, ...), but the Crawl Space won't spawn unless it's below a simple rock.

Layouts

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  Black Market entrance

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  (Rare)
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  (Rare)

Notes

• Crawl Spaces may sometimes lead to a Black Market.
• There is only one crawl space room per floor. Thus, if you find two trapdoors with ladders on the same floor, they will lead to the same crawl space. When you exit the Crawl Space, you will come out from the entrance you came in from.
• There is no map in the Crawl Space, similar to the Black Market, the I AM ERROR room, the Devil Room, and the Angel Room.
  • This is because the Crawl Space does not technically occupy a fixed location on the floor relative to other rooms; Isaac is, in a sense, teleported to the Crawl Space when he touches the trapdoor.
• It is possible to enter Black Market through a crawl space even when there is no path to it. By using two bombs, the player can clip out of bounds and then walk underneath the crawl space room.
• Rocks with Crawl Spaces under them will flash while holding the Shiny Rock trinket.
• The chance to find a Crawl Space upon destroying a rock can be increased with the Stud Finder trinket: 1 in 100 with Mom's Box, 1 in 200 otherwise.

Trivia

• The layout of the Crawl Space is a direct visual reference to the treasure rooms in the Legend of Zelda for the NES.
• Crawl Spaces are referred to within the game files as "Item Dungeons".

Bugs

Bug!	If Isaac's hitbox is small enough (by using One Makes You Smaller pills), it's possible to travel through the walls and ceiling to access the Black Market.

References

The Binding of Isaac: Rebirth
Achievements Challenges Completion Marks Items Trinkets Characters Chapters Rooms Transformations Attributes Bosses Monsters Pickups Modes Curses Objects Seeds Effects Endings
Collection Item Pools Version History Modding Music