Crawl Space

Crawl Spaces (also known as Retro Treasure Rooms) are small secret rooms that can be entered by touching trapdoors with ladders in them. They can be found in 4 / 7 different ways:

1. Using We Need to Go Deeper! randomly (8% chance)/ on certain patterned tiles (100% chance once per floor)
2. Using Rune of Ehwaz randomly (10% chance)/ on certain patterned tiles (100% chance once per floor)
3. Bombing a Clean Bedroom rug (100% chance)
4. Destroying a rock (see below)
5. Using Chaos Card on Great Gideon (100% chance)
6. Getting hit while having Cracked Orb (unknown chance)
7. Using XXI - The World? (100% chance)

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 effects. However, Isaac cannot fly over the walls or floor. Items spawned inside are generated from the Treasure Room Item Pool.

Mechanics

When entering a room pre-determined to contain a Crawl Space entrance, an 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 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.

• Crawl spaces may spawn under variants of rocks.

Layouts

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  Black Market entrance
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  (Rare)
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  Sometimes an item can spawn in a closed-off space, requiring specific items in order to access it.

Notes

• Crawl Spaces sometimes contains another exit on the right side, which leads 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. Creating a Crawl Space within a Crawl Space with XXI - The World? will just take you back to the original one.
• Entering a Crawl Space in the Boss Rush room and exiting it after the time limit has expired will transport you back to the Mom Boss Fight room.
• 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. Possibly related to this, if a player enters a crawl space from a Devil Room, upon exiting they will emerge back in the regular map.
• 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.
• Crawl spaces can appear in Greed mode as well.
• Rocks with Crawl Spaces under them will flash while holding the Shiny Rock.
• The chance to find a Crawl Space upon destroying a rock can be increased with Stud Finder to a 1 in 200 chance.
  • With Mom's Box or a Golden Trinket it becomes 1 in 100.
• Leaving a Crawl Space from any side where no exit exists brings the player to I AM ERROR.
• The Crawl Space spawned by Great Gideon always has the same design even if another Crawl Space was encountered.
• One Crawl Space layout contains two items, one of which is entirely enclosed by walls. The following are ways to obtain the seemingly off-limits item:
  • Teleport to it with Stitches;
  • Grab it with Mr. ME!;
  • Jump through the wall with How to Jump;
  • Absorb it with Moving Box, then spawn it in another room;
  • Clipping through the wall with Pluto;
  • Cloning the item using Diplopia and grabbing the copy spawned underneath.
    • This applies as well for Crooked Penny;
• Be careful when using The Poop, as in certain situations, the poop can block the exit and get you stuck.
• Crawl spaces can be found during the Mother's Shadow sequence.
• Crawl spaces can still be found on floors during the Ascent to Home.
• With Continuum, if Isaac shoots downward in a Crawl Space, his tears lastingly accelerate and can loop for many times (over 20) regardless of his range.

Gallery

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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".

Seeds

PC Q16B 7688 (Southeast corner after starting the first wave)

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. In the walls are much harder to clip through, but it can still be done with high speed and help of the stairs or flight.

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