The iconic view of a dungeon is of a constructed underground complex stuffed full of monsters and loot. There are other kinds of dungeon, though, ripe for adventure.
Designing a megadungeon is hard. If you don’t get the dungeon’s metaphorical foundations right, you are wasting your time.
A good dungeon forces explorers to interact with its terrain features. Dungeons with nothing but smooth floors, featureless walls and plain ceilings realise only a fraction of their potential.
Musty dungeon corridors set with uneven flagstones whose walls are daubed in goblin graffiti are infinitely more interesting than “a dungeon corridor.”
Surely designing a dungeon badly is a doddle – just sketch some rooms out and randomly stock them with monsters and treasure? That’s true up to a point, but taking extra time to consider the dungeon’s ecology is design time well spent.