Staircases are the manner in which you get deeper or climb out of the dungeon. The symbols for the up and down staircases are the same as the commands to use them. A < represents an up staircase and a > represents a down staircase. You must move your character over the staircase before you can use it.
Most levels have at least one up staircase and at least two down staircases. You may have trouble finding some well hidden secret doors, or you may have to dig through obstructions to get to them, but you can always find the stairs if you look hard enough. Stairs, like permanent rock, and shop entrances, cannot be destroyed by any means.
Many secret doors are used within the dungeon to confuse and demoralize adventurers foolish enough to enter, although all secret doors can be discovered by stepping adjacent to them. Secret doors will sometimes hide rooms or corridors, or even entire sections of that level of the dungeon. Sometimes they simply hide small empty closets or even dead ends. Secret doors always look like granite walls, just like traps always look like normal floors.
Creatures in the dungeon will generally know and use these secret doors, and can often be counted on to leave them open behind them when they pass through.