And the winner is ... Megadungeon!
The Apollo's Bones campaign.
When I offered my GURPS group some different campaign concepts to pick from, I didn't expect any of them to get a perfect score, but this one apparently hit all the right notes. Despite the heavy prep required (still working on it four years later!), this was one of my secret favorites that I hoped they would choose.
Wait, what's a megadungeon?
Definitions will vary, of course (what is 'a tall building'?). Let's start with "what's a dungeon?" and go from there. A 'dungeon', to me, is a single location with movement constraints (typically but not always underground) with hostile inhabitants, and some compelling reason for the PCs to go there (loot the treasure, rescue the Baroness' nephew, destroy the evil altar, etc).
A megadungeon is that, but bigger. A single location large enough to sustain at least a dozen adventure sessions; in other words, an entire campaign's worth of adventure gaming in basically one location.
For further reading on megadungeons in the GURPS context, Peter Dell'Orto's Dungeon Fantastic blog has great ideas and links to further resources.
Why a megadungeon?
Several reasons, in no particular order.
1) Nostalgia - So many of the old AD&D modules that I cut my gaming teeth on included a passage that went off the map and invited the DM to place "further adventures" here. Later, as the idea of vast underground spaces and civilizations was refined, this typically became a link to "the Underdark". I think it was the publication of the D/Q-series modules, with their lizard caravans and Drow cities, that really expanded my idea of what could be done with underground spaces. Judges Guild's phenomenal Dark Tower module provided an example of a very large (not quite mega-) dungeon that wasn't just a collection of rooms and levels, but had a history and rationale that was significant to adventuring in it. So, yes, I'd really like to reconnect with the sense of wonder, possibility, and ADVENTURE available in a place that's too big to camp at the entrance and do "day trips" into.
2) Economy of effort - OK, this one is probably questionable. In theory, one big dungeon that uses the same campaign background, supporting town/city/market/NPCs, equipment price list, etc etc should be easier to put together than a bunch of smaller dungeons. In practice, I'm finding that there's some self-inflicted pressure to get it just right that I wouldn't feel with an adventure I know the PCs will enter, leave after a couple sessions, and never come back to. Even with design principles like "town is a safe place where adventures don't happen", I feel a need to build the areas outside the dungeon with enough depth and integrity to support a campaign's worth of roleplaying, not just a session or two. So, this one is probably a wash.
3) Heroics and isolation - One of the major barriers to storytelling in the modern era is 'the cellphone problem' - why don't the protagonists just call a taxi or the police? The answer to this question drives many of the tropes we're used to seeing in TV and film. From "there's no signal" to mafia dramas and heist capers where the police are the enemy, the end result is to force the protagonists to rely on their own resources to succeed or fail. Similarly, a small dungeon can permit an adventuring party to quickly flee out the entrance if they get into trouble, whereas a dungeon large enough to force an overnight stay requires more commitment, and can create harder choices for the players as they gauge risk and manage resources like food, water, and light.
Why is it called Apollo's Bones?
Because Apollo's dead, murdered two hundred years ago by the titan Krios after his escape from Tartarus. Apollo's corpse, hurled from the sun chariot, fell to earth in southern Gaul, carving a vast pit into the ground. The death of Apollo ushered in the Age of the Red Sun, in which crop failures, eruptions of undead, and monster incursions have tested humanity's survival. Apollo's divine flesh, blood, and bones carry magical potency, and his fall attracted treasure seekers and mystics, who built a mine where his body fell. A century of activity left a few rich, and many more dead or insane, as the miners began to encounter odd caves and structures underground, and the attentions of their denizens. Now too dangerous for organized mining, the area surrounding the abandoned mine is an undead-haunted wasteland.
The group I play GURPS with runs with four regular players and a rotating GM, plus an occasional drop-in. Starting PCs will be 150 pts base, plus up to 25 pts in disadvantages,and 5 pts in quirks. This is significantly lower than the gung-ho Dungeon Fantasy 250+50+5, as I'm aiming for some of that "zero-to-hero" feel that old school D&D offered.
Similarly, I'm setting TL at 3, and sticking to medieval tech with less of the Renaissance trappings that tend to sneak in. No fencing weapons, articulated full plate harness, or portable spring-powered clockwork geegaws. I'm also planning on a few houserules that will appear in future posts.