DDP's Sprite Workshop

[DragonDePlatino]

In Pixel Dungeon, doors swing open when creatures stand on the same tile as them. This lets them see in rooms but lowers their evasion to 0% for a turn and makes them very vulnerable to fire attacks. When they walk off the door tile, it closes behind them.

A receding metal door would be interesting, though. In addition to the Sewer, Pixel Dungeon has a Prison, Cave, Dwarven City and Demon Hall area. A receding metal door might work best for the Prison area.