Cass
There's a door on the third floor stairwell, unmarked, deadbolted from some angle you can't see. I walked past it for two years assuming storage. Then one day someone had propped it open with a folding chair and inside was just... more stairwell. Continuing up. It had a door number and everything, like it belonged to a whole separate building logic. Nobody I asked knew why it was locked. Eventually they fixed the lock and I stopped thinking about it, mostly.