I'll be honest right off the bat; I love megadungeons. If I could spend the time and effort required to run one all the time I would. They are an awesome relic of a bygone era that I love to return to whenever I can convince my players to enter one. But before I get too far ahead of myself, what exactly is a megadungeon?
A megadungeon is more than just a really big dungeon, though it certainly is that. It is an entire ecosystem, a complex world that while different than the world on the surface, has similar considerations. They can be so large that entire cities can exist in their rooms, and dozens of factions of inhabitants will fight over resources. The megadungeon is built to house creatures from goblins to dragons to beholders. Whether friend or foe, there is something for everyone within.
Megadungeons first came about in the days of TSR, when the people creating the modules put a level of effort into their products that one rarely sees in officially sanctioned work these days. This may be personal opinion, but I feel that in the old days of D&D, when a dungeon and locale was released, every room, every trap, every monster was carefully detailed and ready to go for the Dungeon Master to use. Now, it seems there is a lot of burden on a DM to make things up on his own. While this of course is fantastic for those who enjoy the minutiae of dungeon building, for the typical DM with a job, a family, and a life outside of the game, one rarely has time to make a dungeon, let alone a megadungeon from scratch. Even now, most claims of modern megadungeons being all-inclusive fail to deliver; instead merely creating a map with a story, leaving up to you to fill.
In a megadungeon, the players seek to find riches and glory beyond their wildest dreams. They may face outlandish traps, mind-bending puzzles, horrifying monsters, and suffer fates worse than death. More-so than any other location, a megadungeon represents lethality. A party goes down deep into the earth, and may never return. They may never be heard from again, or be turned into ghastly undead for another party to face. Those who do return are stronger for their troubles, and usually much richer. That is really what a megadungeon is for: to test one's mettle, and get rich doing it. It is a balance between risk and reward. Life may be safer on the surface, but only the largest dungeon in the world has the glittering gold that makes an adventurer's mouth water.
The effect that players have an a megadungeon is up to the DM. Most dungeons are small enough that when a party wipes out a room, nothing happens if they come back to it later on. But a megadungeon is so massive and has so many creatures and factions within it, that a party might permanently change the political tide or ecological situation in an area. Killing the orc band that inhabits a section may leave it open for beholders to come in and make up base. Befriending the local duergar inhabitants may give the party cause to eradicate the drow camp, thereby allowing a larger influence for their allies. What happens to a dragon's hoard once the players take as much as they can carry out? The locals take it! Retrieving the stolen treasure might be an adventure on its own. No matter what happens in a megadungeon, the players can have a huge effect there, and there are literally no end to adventure opportunities.
Of the many available flavors, my favorite megadungeon is Undermountain, a fantastic beast of a dungeon with a great story involving the mad wizard Halaster Blackcloak. It's pretty much everything that defines old-school D&D adventuring, complete with insane traps, ridiculous scenarios, and monsters that are too big to fit in the dungeon. Most importantly of all, the dungeon builds in an excuse to why people cannot teleport throughout it, since Halaster has imbued powerful magic into the dungeon itself, barring such magic, except of course his own. This is great as it forces even high level players to do it the old fashioned way: walk. This megadungeon is alive and truly an amazing feat. Unfortunately, subsequent updates to 3rd and 4th editions of D&D have left much to be desired, with significantly less detail being applied to each new iteration of the dungeon.
Other great megadungeons include Castle Greyhawk and Rappan Athuk. The former is written by none other than Gary Gygax himself, while the latter concludes with an epic (and intentionally unwinnable) fight with Orcus, the demon lord of the undead. If you're interested in Rappan Athuk, it has been converted to the OGL system, but I don't believe Castle Greyhawk has. Also, I must point out that Monte Cook, one of the designers of the OGL and 3rd edition, has created a website called Dungeon-A-Day that sought to create a massive twenty level dungeon. I don't subscribe to the website myself, but those looking to find a complete and 100% detailed megadungeon may wish to look there. There is a yearly subscription fee, but for the level of completion there, I would highly recommend it.
On a final note, I will say that megadungeons are not for the feint of heart. They require a lot of time and effort to set up. However, they can lead to endless fun in an RPG game, and will provide your players with hundreds of stories by the time they are finished. Just be prepared for a game that lasts several years. Thanks for reading, and stay tuned tomorrow for "N is for NPC".
The Megadungeon Blog