The entrance is magical. You appear atop the hill, in a circle of twelve sycamore trees, the center of which is a pool that slowly drains, revealing a staircase that heads down into the hill. The land beyond is shrouded in mist, though you can hear a lake lapping. Excalibur isn't actually there. It's just a prop.
Within, first is just a simple tomb, small, unelaborate, with some clues to what dangers lie ahead.
Thereafter, what happens?
I definitely need hints that vampires got in. Maybe something as simple as a lot of ash. There was running water, but it's been disabled. Vampires could get through in mist/rat/bat form, but the PCs will have to fix the water system.
King Arthur has to be there, and has to fight them with Excalibur because he's turned evil. They need to heal the true king some time during this fight, with the grail. The fight has to last at least 10 rounds.
The bad guys, or at least a few of them, need to show up to try to stop the PCs. I need a sufficiently interesting location for a climactic battle. Key elements that must be there include:
1. A place for someone to be healed.
2. A pool or water of some sort. Perhaps running water which you could submerge a vampire in. And at the end, a horrible figure can rise up from the lake of blood (an undead lady of the lake) trying to destroy the Dungeon of Avalon before they cane escape. Because you've got to have a 'flee the collapsing dungen' scene.
3. Cover.
4. Something mythic.
Before this, there should be three challenges. A test of arms, a test of wits, and a test of faith. Very straightforward.
The black knight always triumphs! Some sort of shadow knight.
A clan of gnomes have been bound here so that they run around and lock doors and disable mechanisms. There's a complex device that opens a door while simultaneously keeping the area from being crushed with flaming peat, and it requires several different manipulations in order to activate. The gnomes insult the PCs from hidey holes, and cannot be hit since they're mostly illusions anyway. They can be distracted if you insult them back, though. If you try to break the mechanism, you'll probably kill yourself.
The test of faith should be obvious. Seriously, the players should know that I won't kill one of their PCs. But they might just think I'm serious, and that yes, really, you must offer up your life in order to reach the king and the leyline locus of healing. There might be some sort of statue representing Mordred and Arthur falling upon each other, and the pious person might need to fall upon a blade in order for the others to gain entry. But you don't die.
Some other small tests might be things like resisting the temptation to steal treasure.
I'd originally envisioned this as a giant complex, but since I rather want to finish the campaign, three vignettes of trials should work. Now I just need to figure out the specifics.
