Basil's Home
This section or article contains spoilers about Heartbound's content or story.
This is a unknown location in Animus. . . somewhere.
Home or Hideaway of Basil.
Only currently accessible by altering the save file.
Entering the room, even in this way, will unlock the Hidden Hideaway achievement.
Also, I had nothing to do with finding this.
Entering
To enter this place (the only way we now for now), you must change the save file's second line from whatever it says to "animus_basil".
You can edit the save file in Notepad.
To get to your save file, press the Windows key + r and type into the prompt "appdata". From there, follow this path [AppData/local/Heartbound/heartbound_save7.thor] in the Windows Explorer Tab and then just edit it.