The game doesn't know offhand why a door is hidden. For example, there are a number of places where a set of bushes or brambles acts as a 'door'. Similarly, something could be concealed by magic, which dwarves aren't good with.

It's possible we could mark doors with some sort of dwarf-detectable flag, or hope that area writers remembered to assign a correct material to their door, and have it only work on doors made of stone.

valguarnera@carrionfields.com