Pathfinder Online: Thornkeep and The Emerald Spire are Pathfinder products created to help promote to Kickstarters for the mmo, Pathfinder Online. Unfortunately, despite the Kickstarters, the mmo has run into some funding issues. That being said, the two books to come from the kickstarters are a lot of fun. I didn't back either Kickstarter and I don't care for mmo's, but I did snag both books.
The first Thornkeep is a hybrid setting and adventure book. Detailed within the pages is the titular Thornkeep, a wretched hive of scum and villainy in the River Kingdoms, and the the surrounding area. The area is cool because it contains Azlanti ruins (think Atlantean for those unfamiliar with the setting), as well as the ruins of a goblin kingdom (and let's be honest the goblins of Pathfinder are one of the coolest things). After the setting material we are given several short, interconnected adventures that take place in an ancient dungeon beneath Thornkeep. Each section is written by a different rpg superstar: Richard Baker, Jason Bulmahn, James Jacobs, Erik Mona, and Ed Greenwood.
As it states on the cover, The Emerald Spire is a Pathfinder superdungeon. I guess they didn't want to use the word, megadungeon. The hardcover discusses Fort Inevitable (an interesting town ran by Hellknights), which can serve as a homebase for the party. Most of the book discusses the levels of the dungeon, itself. Like Thornkeep, it features many big names in the industry: Keith Baker, Rich Baker, Wolfgang Baur, Jason Bulmahn, Ed Greenwood, Tim Hitchcock, James, Jacobs, Nicolas Logue, Erik Mona, Frank Mentzer, Chris Pramas, Sean K. Reynolds, F. Wesley Schneider, Michael Stackpole, Lisa Stevens, and James L. Sutter.
Both books seem like they'd be a lot of fun to use and both are set in the same part of Golarion (the Emerald Spire is mentioned in Thornkeep). Want an old school dungeon crawl with a modern twist? Check out The Emerald Spire and Thornkeep.