I'm starting with a fairly famous one, "Rappan Athuk (Reloaded)", which you can get from the finely crafted link there.
About Rappan AthukRappan Athuk, per its introduction chapter, is "nothing more and nothing less than a good, old-fashioned, First Edition dungeon crawl updated for Revised Third Edition play." (All editions referenced here are D&D, not GURPS or Shadowrun or anything like that.) It was released by Necromancer Games in 2000 with some supplements and web material coming out in 2001, and re-released in 2006 in an expanded (Reloaded) edition for D&D3.5 that included all the previously published materials and some additional levels.
Rappan Athuk Reloaded consists 3 books. The first details the namesake dungeon, all 31 levels and sublevels, and the surrounding wilderness. The second book contains the monster and NPC statistics. The last book has the relevant maps.
The concept of Rappan Athuk is simple: two centuries or more ago, a group of refugee priests of Orcus carved an underground complex beneath a hill and eventually made a mausoleum and graveyard above it. For a hundred years, curious and crazy delving bands have been exploring the complex and mostly dying horribly. Still, rumors abound of great riches somewhere in the complex, so delvers keep venturing out.
The IntroductionThe first chapter explains what Rappan Athuk is and lays out the conventions for numbering rooms, statting out monsters, and describing the standard characteristics of a given floor (in terms of suggested PC level, corridor and room height, normal light sources, etc). This is pretty standard stuff, though I do appreciate that they had a standard format for describing basic information about each level and used it consistently in the following chapters.
The Introduction chapter also includes a table of 60 rumors - 44 are mostly true, and 16 are generally false. There's a weird rules quirk in that most PCs have a chance of knowing 2 rumors, but wizards, clerics, and bards have a chance of knowing a third. Druids and sorcerers don't get that chance, and there's no provision for PCs to go seek out more rumors by making Gather Information checks. (As an aside, the conversion of this adventure to the D&D3 ruleset is often a bit weak, but since I'd have to convert it by ear to GURPS if I were going to use it, I don't really care beyond some minimal snarking.)
The rumors are generally useless. Most of them are so vague as to be meaningless: "Giant scorpions guard the way to the tomb of a fell king" provides what information, exactly? If the rumor specified a level, or mentioned some kind of weakness of these particular scorpions, that'd be something, but as it is, there's nothing for the PCs to do with it.
Another problem with the rumors is that they don't cover things that you'd expect them to. The mausoleum has a very lethal, nearly unavoidable instant death trap unless the delvers use a specific magic key that can be found nearby. This is the kind of thing that you'd hope previous explorers of the damned dungeon would relate, not "A great city of Goblins lies deep in the complex, and they are followers of Orcus."
Wilderness Areas: Dying Outside the DungeonThat's the actual name of the second chapter. It's actually a reasonable wilderness area: a coastal region, with some lowlands lying between the sea and a forest, with a semi-patrolled trade road providing access to Rappan Athak and points beyond. Each of the major terrains in the area have their own write-up, including random encounter tables with encounter write-ups and a few monster lairs. The encounter tables have a nice trick where the base roll (usually a 1d10) is modified by location and day or night, so it's possible to sometimes encounter foot patrols of the local governments in the swamp, but only in daylight and within a few miles of the trade road. Conversely, will-o-wisps only show up at night and deep in the swamp. It's very elegant.
As nice as that is, there are the bandit groups. I quote from the text:
That's the introduction for an encounter with an ogre and 112(!) kobolds. So after a potentially difficult delve that results in recovering pocket change, the delvers get ambushed by an insurmountable number of kobolds and robbed of their weapons and new found loot. That's to teach them to not overextend themselves, supposedly. Looking at that from the perspective of a player, it teaches me not to play with this GM ever again. How is that encounter supposed to be fun?This encounter can be used when the party first exits the dungeon with a load of treasure. The purpose (other than a lot of fun for the DM) is to teach them a lesson about over-extending themselves.