Look For Secret Rooms
How to Find Secrets in Binding of Isaac: Rebirth
You likely have stumbled across a secret room by accident in Binding of Isaac: Rebirth. Maybe a random bomb or explosion went off in the right place, you were greeted with a short tune, and found yourself in an unmarked spot of the map.
These rooms almost always have items, slot machines, beggars, or a wealth of consumables to choose from. They’re great, but only if you can find them, which might seem difficult and costly since you usually must spend a bomb to open them yourself.
Fortunately there is a logic behind their placement in the procedurally generated maps throughout Binding of Isaac: Rebirth. When exploring, look for a section of the map where three rooms encircle a blank space on the map, or where four rooms encircle but leave a gap as pictured. Put your bomb on the wall you think leads to the secret room, right in the center, and with luck, the wall with break and lead you to treasure!
There are also Super Secret Rooms that litter Binding of Isaac: Rebirth. These offer much higher rewards and loot, but are much more difficult to find, as they will only be attached to one room.
If you really want to hunt down a Super Secret Room, here are the rules: They will only have one entry, and that entry will never be an special room (item, boss, shop, etc.). The entrance must also be directly accessible, meaning no rocks or obstacles where the door should be. Finally, they are usually close to the Boss Room so long as the other conditions apply.