I recently dug up a couple of old dungeons that I designed back in the day. Was still flush with the excitement of the Little White Box of D&D books. The first was four levels. The second was six. Even found some player character sheets that prove I actually did GM them. Those were fun days...er, nights, actually. No worries about context or big campaigns. Just bizarre dungeons into which we waded and hoped to survive long enough to reach that lofty third or fourth level. Slimes, traps, molds, orcs, goblins, wraiths, gelatinous cubes, T-Rex conga lines...
I hope I will soon run across my biggest dungeon. I can still visualize the first graph paper layout with its bridge across the wide cleft in the rock just outside the entrance.