The Binding of Isaac – How to Unlock the ‘???’ Character

The doors are tied to your health. The door will only be open if you have full health. However, the temporary HP boosts (blue hearts) can serve as a equivalent of the missing red hearts.

For example: If you're missing one red heart but have one blue heart the door will open. But if you're missing two red hearts and only have one blue heart the door will still be locked.

The music files are located in whatever drive you installed Steam on, then this path:

\Steam\steamapps\common\the binding of isaac\The Binding of Isaac Soundtrack

Your files should be there and ready to play! Alternatively, you can go to the steam client and look under library > music, and see all the purchased soundtracks you own.

If you're on a Mac you'll find that path in [Home]/Library/Application Support/Steam.