Library

Libraries are rooms that must be opened with a key. Items from the Library item pool can be found within, among other things, such as Cards and/or Runes or even enemies. Libraries have a 5% chance of appearing each floor. Certain Library layouts can only appear after unlocking certain store upgrades from donating to the Donation Machine.

Layouts

The following room maps were made using Basement Renovator for cleaner viewing. Items generated in these rooms pull from the Library item pool.

ID	Shop Level	Weight	Contents
0	0	1.0	Two items side-by-side in the center, and one cobweb each in the bottom left and top right corners.
1	0	1.0	One item and two Cards.
2	1	1.0	Two items and one Little Battery.
3	0	1.0	One item and two random batteries.
4	3	1.0	Three items, surrounded by four Fire Places.
5	4	1.0	Five items, one in the center available for free, and four in the corners trapped behind iron/key blocks.
6	1	1.0	Two items, one each in the top left and bottom right corners, and two urns, one each in the bottom left and top right corners.
7	4	1.0	Four items, trapped behind iron blocks and spikes.
8	0	1.0 0.25	Four Cards.
9	2	1.0 0.5	Two items, with a Key Master in the middle, and two cobwebs adjacent to the latter.
10	4	1.0 0.5	Five items at the top, all trapped behind iron/key blocks.
11	0	1.0 0.5	One item, surrounded by Maggots.
12	0	1.0 0.25	Four Cards in the middle, next to a cross made out of rocks.
13	0	1.0	Two items at the bottom, surrounded by cobwebs, urns, and red Fire Places.
14	0	1.0	Two items: one in the middle, next to two Fire Places, and one on the right, trapped behind rocks.
15	0	1.0	Closet-sized room with two items. Closet-sized room with one item.
16	0	0.5	Two items, a Bomb Bum, and each corner has a 50% chance to be either a cobweb or a random bomb.
17	0	0.5	Two items and a Wooden Chest.

Notes

From the outside, the library is identical in appearance to the Shop. One of the ways they can be distinguished is if Isaac has a mapping item such as Spelunker Hat or The Compass. Generally, the library will be closer to the starting room than the Shop.
- The library now has its own unique door.
Once all items in the Library item pool have been picked up, items from the Treasure Room item pool will appear instead.
Libraries are particularly useful for acquiring the Bookworm transformation.
NO! now replaces all activated items inside the Library with passive items, which prevents all Library items from appearing other than Book of Virtues.