Recommend large, complex, logical dungeons

Question

I did not find the right question, so if this has a duplicate, simply relink this question.

As a treat for my players I would like to master a very good dungeon. Good means:

• It should be free or so good that you would spend $10 bucks to buy it.
• It is quite big and/or tricky to understand.
• It has a valid purpose to exist (Backstory, who build this, why isn't it (completely) plundered, who are the inhabitants)
• No logical errors / plotholes (You know: No missing bathrooms/food/lodging, no traps in often used environments, no 50 monsters living peacefully together in separate rooms, but attacking players on sight).
• It has refined NPCs who have their characteristics, purposes and destinations.
• Rightly done, it builds a lot of suspense.

I hope that this is specific enough; perhaps I am looking in the wrong places, but really good dungeons seems to be rare.

Disclaimer: "In media res" is really cool, but My players like their characters, so "Tomb of Horrors" is out of question.

Setting is fantasy/medieval (we are playing The Dark Eye), but there is no problem to adjust the dungeon if the core adventure is OK.

Answer 1

Dyson's Dodecahedron has a number of really nice self-contained dungeon adventures, some of them are award-winners. Scroll down the page to see them.

For your purposes, the one I would recommend is "The Sewers of Travon"

• It is free. (+)
• It is large: (+) It spans under the entirety of a largish city (underground).
• It has a valid purpose to exist: (+) It is a sewer system, basically.
• It has no logical errors or plotholes: (+) It is easily suited to any city with sewers and thieves.
• It has refined NSCs: (-) The characters and forces are written up vaguely, so you must color them up, but their relations are described.
• Rightly done, it builds a lot of suspense: (+) Sewers are creepy already, they're full of gross stuff, and did I mention the ghouls...?

Answer 2

A very interesting dungeon I've run with my group was the Halls of the Mad Mage, by the Alexandrian. It plays around a lot with non-Euclidean geometry (an everflowing waterfall, for example, and a set of stairs where going up and down take you to the same room - this was a lot of fun for my group when they tried to figure out what was going on, and it's definitely tricky to understand.

It's designed for a fantasy setting, but it's mostly system-agnostic (the monsters aren't statted but there is a gateway to the Ethereal Plane). You may want to change some of the creatures if you have a very high or low level party. There aren't any NPCs (as in, people to talk to). It consists of 26 rooms (the 20 on the map, and then the 6 ceiling rooms).

This isn't necessarily a perfect fit for your question as-is, but if you were to tweak it a little or merge it with a different dungeon I think it would be ideal, and it's at least OK based on your requirements. It's probably my favourite dungeon that I haven't made myself, and it's free.

Suggested improvements

Add an NPC or two and some more monsters appropriate for your PCs levels, as it's not very combat-heavy as-is. There are many rooms with interesting contents that aren't of the 'goblin in a 10x10 ft. room' variety, but for players who want to stab things there are sparse pickings.

You can also bolt on extra dungeon space from the underwater area in the pool, and have some of it be in the Ethereal Plane if you want to. This was made as part of a 1-page dungeon challenge so it's quite short in some places, but I enjoyed fleshing it out on the fly since the design made it easy to get ideas for what else was in there. Despite the small amount of space, it took my group 2 sessions to get through it.