Well you may remember from earlier posts my players in my previous campaign having explored a dungeon called "Valarn's Vault". Well I've decided to revisit this dungeon, applying the lessons I've learned about dungeon creation since then. So I'll rewrite the dungeon, pretty much from scratch. I will be using Pathfinder and am thinking of setting it in some undetailed part of Oerth outside the Flanaess, or a world of my own creation.
The Vault is a fortress that belongs to a powerful necromancer on an island not far of shore from a small fishing village in the tropics. The upper works contain a large garrison of various kinds of undead, however there is a back entrance to the far less dangerous storage area. The upper works are basically a "lair"-type environment, so aren't really suitable for low-level adventurers, but the storage area and lower levels are a more normal dungeon environment, so adventures here are not going to bring the wrath of every creature in the area on they're heads. Below the storage area is a series of catacombs that contain many undead of various kinds. I'll have fun utilizing all the various obscure kinds of undead in my monster manuals populating this area. The third level I'm thinking will probably be a series of laboratories, filled with all kinds of weird monsters, including templated monsters of various kinds. However, I'm thinking I might want to save that theme for a lower level, since I'd want to include more dangerous creatures like golems. The lair of Valarn himself will either be on the twelfth or lower level or a sub-level attached to it. Perhaps his lair will be a demiplane connected to the dungeon by portal. As for other levels, at the moment I'm focusing on the first three as Gary Gygax suggests in Volume 3 of OD&D, "The Underworld and Wilderness Adventures".
As for difficulty I am not going to be adhering strictly to the rules in Pathfinder. Like in old school games it will be somewhat challenging. It would in fact be likely to encounter ten goblins in a single encounter on the first level of the dungeon. However the PCs would be well equipped to handle such encounters, as Pathfinder characters are fairly powerful and it will be assumed that they will bring along non-player character hirelings to help them, including warriors.