Sorry for the delay, I had intended to do one level of the dungeon every day. Unfortunately, offline life is not cooperating. However, here is a description -- taken from my old design notes -- of the second level of my Under the Pyramid megadungeon from the 1970s.
Before I start, I need to add a bit of information to my description of the first level. In each of the goblin camp areas, there is a temple to a serpentine deity. One faction sacrifices a captive on the new moon, the other faction on the full moon. If there are no captives, a member of the tribe is selected at "random" so there almost always are captives. The altars have strange symbols that look like humans with snakes for heads.
The second level was a maze of passageways, open chambers, and hidden rooms. The passageways and chambers were empty except for wondering monsters (25% goblins from level one, 25% serpent men from level three, 50% random from the OD&D charts). Most of the many hidden rooms are empty except for odd remains of contents and former inhabitants. There is a 2% chance per person/per turn searching a room that some random bit a treasure will be found. There is a 1% per turn after the first spent in a hidden room that some party member will be exposed to a disease (save to avoid) that causes a loss of 50% of the character's HP to fever and exhaustion under cured by magic or a week's bed rest.
Most of the passageways and chambers have unnerving and even obscene reliefs carved on the walls in a one foot band near the ceiling.
One hidden room contains the statue of a young girl in the center of a fountain. If anyone drinks from the fountain they can hear the statue whispering insanely about evil monsters from beyond time and space. If a drinker makes his save, he will also be cured of 1d6 points of damage. Another hidden room will seal completely (the door disappears) once the party enters. The door will reappear in 1d10 turns. There is no way out of the room (short of a wish or divine intervention) while the door is missing. Random monsters appear in the room every turn the door is missing. They are illusions, however. One hidden room is a circular pit with a staircase winding down. It winds down several hundred feet before plunging into water. Fifty feet further down is a locked door that will not open without key found on level 5. Inside the room is the crypt of a vampire with lots of treasure.
There is a hidden complex of rooms on this level that is the former home of a evil cleric and his followers. They are now all ghouls. Very hungry ghouls. A second hidden complex rooms the lair of a pair of Ogres and their bugbear servants. They just want to be left alone. A diamond worth 10000 gp is hidden in a trapped chest behind a secret door. The Ogres aren't aware of it, but one of the bugbears is.
Several staircases lead down. Two lead to level three. One leads to level 4 and turns to a slide once everyone is on it.
Coming soon: Level Three.