The book has a slightly bumped corner. (see photo)

The Castle Xyntillan sourcebook features an adventure for 1st to 6th level characters, set across three massive levels of a complex megadungeon. The adventure's stats are compatible with various OSR systems, such as Swords and Wizardry. A separate map supplement is included.

Still hesitating? Read this review by Bryce Lynch. "This however IS the only adventure you ever need. You could run a party through this for YEARS, with more than enough information present to riff on. A perfect OD&D product, with whimsy and wonder without going off in to Funhouse territory."

The book is in English, hardcover, and has 132 pages.

Castle Xyntillan is one of my personal favorites from the current OSR scene… A "spooky" castle designed as a megadungeon. "Spooky" is in quotes because it's that stylized, humorous kind of spooky – singing skeletons in uniforms, animated statues, talking paintings, eerie wailing, stuffed monsters… The building is incredibly vast (300 locations), filled with all sorts of traps. It's far from just combat; there are plenty of non-combat puzzles, weird magic items, and 60 NPCs (!). It's obviously not "realistic," yet the game still has its own internal logic, thematic circles, recurring motifs, and players can figure out how it works…

Megadungeons often run the risk of becoming repetitive, where doing the same thing over and over stops being fun. I think Xyntillan successfully avoids this – later, harder-to-reach passages change thematically, the difficulty naturally increases, and at one point, the environment around you shifts completely, almost as if you've ended up in a fairy tale. The module also has several built-in "quests" that players can discover and solve, giving the game structure so it isn't just aimless wandering. The evolving relationships with members of the local Malévol family, who have their own grudges and schemes, add further dynamics.

In short, Xyntillan is a brilliant example of level design for an open, sandbox game. You can go anywhere and do anything… and no matter where you go or what you do, an interesting story thread will emerge. Various locations are interconnected, reference each other, and influence one another, while different elements or "tasks" encourage further exploration…

From the review by Jiří Petrů on Rpgforum.cz