I'm creating a large dungeon for a 3rd level party in a custom campaign setting. The dungeon is the ex-lair of a Black Dragon (old, not sure which category, but old), which has been reinhabited by various dungeon denizen. The dungeon should be quite large, with at least 5000xp available -- this will likely take several gaming sessions to clear.
Does anyone have any good dungeon ideas that have been successful? I'm looking for interesting traps, encounter setups, loot, map pieces, anything really. I'm sure I can create such a dungeon, but I want to make it really interesting, so I thought I'd open it up and see what you guys suggest. Anything from EL 2 to EL 6 is good... maybe more if there's a smart way to defeat it at lower levels.