Step 1The Best of the Journal: The Pettigrew Selections. This determines the nature of the Saturday Night Special. Although this above table is designed for use for Tekumel games, it should be useful for most mileus. Results may refer to an ancient/ruined City, Palace, Fortress, etc., or a discrete portion of the megadungeon being used for the generated purpose by the current inhabitants (City = Warren of Derro; Palace = Pleasure Den of a Rakshasa; Fortress = Secret Headquarters of an Assassin Cult; etc).
Note that I strongly recommend the aforementioned The Pettigrew selections as a random megadungeon element generation resource, available from Tita's House of Games.
Also note that shrines and temples should have a fair chance of containing some fabulous treasure that horribly curses those that thieve it; a wonderful horror comic and pulp fiction cliche that seems woefully underrepresented in D&D.
I interpret Wizard's Tower to represent a magician's lair and not necessarily a subterranean tower; although an ancient tower buried deep in the earth by the ages or a tower in a gigantic cavern are both pretty cool.
For my usage Canals means constructed or artificial subterranean waterways: sewers, the Black Reservoir, cave rivers all fall in this category.
Nexus Point is a technical Tekumel term for "transdimensional wormhole portal thingy;" in the context of this method we can use it for teleportals, micro-planes, dimensional gates, time travel device, etc.
In the original article Ancient Tunnel refers to the Humanspace Empire era subways tunnels deep in Tekumel's crust; for non-science fantasy-ish campaigns they obviously refer to Atlantean or Lemurian equivalent relics.
Generate a name for the special with the Beyond The Black Gate - Random Megadungeon Area Name Generator.
Use Dave's Mapper to generate a map of the area of the special; note that you can turn on a 10-foot grid with the buttons along the top. This serves as a workable maze generator, and this does the trick for caves.What I do is generate a geomorph-map and than only use the portions that appeal to me while rearranging elements so as to remove the regular corridor placement. For most specials you probably only need a handful or two of rooms, for usage with Step 4 you will need roughly 8 to 20 rooms (d6+d8+6?).
Using the elements generated in Steps 1, 2 & 3, think of a theme for the Saturday Night Special. For example: On level 6 of the megadungeon I generate a result of "Palace," the name "Screaming Archmaze of the Bone God," and with Dave's Mapper and the maze generator I cobble together a sprawling maze. Obviously the luxurious yet labyrinthine domicile of some sort of powerful undead aristocrat with a a functioning small cult.
Now go over to Playing D&D With Porn Stars and Read This. What you do is come up with lists of monsters, traps and treasures appropriate for your Saturday Night Special, start with the first room and work your way to the last room dicing up the contents as you go.
For the palace maze of the Bone God I come up with the following monster list off the top of my head.
8 - Villain: The Bone God, the Lich-ified remains of a God-Emperor from ages past
7 - Lieutenants: Hoochie-mama Vampire consorts
6 - Guardian Beast: Pet Froghemoth
5 - Assistant Managers: Mummy Cleric
4 - Tough Guys: Cultists with Cleric or Magic-user leader
3 - Grunts: Talkative zombie guards
2 - Servants: Dancing & singing skeleton butlers & maids
1 - Vermin: Eye Dropper
Note: Yes, I pretty much come up with the idea of putting a Froghemoth in every dungeon I think of, regardless of how wildly inappropriate it is.
Flesh out with Tricks, Traps and Empty Room Design from the Hack & Slash blog. Also, the Wilderness Hexploration Document from the New York Red Box forum has a decent temple generator as well as other random generation resources, you could use the Island tables from it to determine what's on a island in a Canals special.