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In-game, I'd say that any previously-delved dungeon will have some of these carved or drawn on the walls. Some might be misleading, some might be no longer accurate, but they should be true enough that they can be an aid to players' navigation and help them in making choices. Compare "there are passages to the north and west" to "north passage is marked 'ooze territory / safe campsite'. west is marked 'disabled trap / monsters can be reasoned with / don't look behind you'".
They're pretty helpful on the DM side too if you need quick ideas for rooms.