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.
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.