There isn't much to Area 28, let's do two rooms today.
Area 29 The Valves of Mithril
A pair of huge mithril doors stand at the top of the stairs described in Area 28. And I mean huge. The doors are fourteen feet wide, twenty-eight feet tall and three inches thick. No wonder we hear stories of adventurers trying to steal them. These doors are almost certainly the most valuable things in the Tomb!
You'll be surprised to learn that the doors are "absolutely spell and magic proof." The module doesn't say if its immune to a thief with a high lock picking skill. Go ahead and be a rat bastard and say it is.
There's a keyhole right in the spot where the two doors meet. You can see it in the illustration provided for Area 28.
http://www.wizards.com/dnd/images/ToH_Gallery/ToHGraphic28.jpg
The keyhole is set in a "cup like depression, a hemispherical concavity." Basically, it looks like somebody took an ice cream scoop and dug a dollop out of the doors. It isn't clear how big this "concavity" is, but it looks fairly sizable in the picture.
If you overcome your
Antipathy and grab the Second Key, you might think it goes in this door. Zzzzap! Take 1d10 points of electrical damage. Hmm. Maybe the First Key, the one that was under the slime back in Area 19 will do the trick. Zzzzap! Take 2d10 points of electrical damage.
The trick is use the Scepter from Area 25. Poke the gold end of the scepter into the cup like depression, and the doors swing right open! Poke the silver end into the doors, and you'll be teleported back to Area 6, naked as the day you were born.
Maybe the players decide to bash down the doors? Well, if the doors are cut with a sharp weapon they start gushing blood like the elevators in the Overlook Hotel. In 20 minutes, blood will fill the room to the ceiling. The module provides a list of several spells that players might cast at the gushing blood. Each has a different effect; some of them seem pretty far fetched. Also, any kind of fire, even the torch you've been paying your henchmen to carry around, turns the blood into poison gas that kills everybody in the room, no save.
IMO: Obviously, the players are expected to try the Second Key on the Mithral Valves. It won't work, and somebody will take a relatively trivial amount of damage. My guess is that lots of groups will get confused and burn a lot of time monkeying around with the Second Key here.
Acererak has told us that the Throne in Area 25 is "key and keyed." We've already seen the Scepter open one secret door. Arguably, those are clues showing the right way to get through the doors. The concavity could be a clue as well, particularly if the DM describes it in a way that connects it back to the Scepter.
How are the players supposed to know which end of the Scepter to use? The silver end worked back in Area 25, but it doesn't work here. The general rule in Area 25 seemed to be "like touches like." Touch the gold end of the Scepter to the gold crown. Touch the silver end to the silver crown on the throne. Mithril is silver, nothing in Area 29 is made of gold, so that pattern fails here. Am I missing something?
I love the image of the doors that gush blood, but how likely is it that the players trigger that trap? Assuming they thought to use force, I'd guess that most groups would try to batter the doors down. The module is fairly clear that the doors only gush blood "if cut by a sharp weapon." Who tries to cut through a metal door?