A Strange Door is an unlockable room in The Binding of Isaac, added in the Repentance DLC.

A Strange Door appears in the starting room of the second floor of Chapter 3.

It contains a trap door leading to a special version of Mausoleum/Gehenna II, ultimately leading to the Ascent path and The Beast fight.

The door requires and will consume either The Polaroid or The Negative.

Given the fact that Mom's Boss Room does not have an exit, Isaac must teleport out upon acquiring one of the items. To accommodate this, a Marked Skull is guaranteed to appear somewhere on the floor, which drops 0 - The Fool when destroyed.

Alternatively, the door can be opened with the Faded Polaroid, Broken Padlock, Cracked Orb, Soul of Cain, or Sharp Key.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this room for the previous Repentance version, check this page instead.

Defeat Mother.

The A Strange Door does not have an associated item pool.

• Check out the room description on the external Isaac Wiki.