Patrick Wetmore's Anomalous Subsurface Environment, the first level of a gonzo megadungeon and it's amazing. I've been reading it in between my other activities and I'm finding it hard to put down.
Since I haven't read the whole thing in any depth, I'll save my hyperbolic comments till I can write a formal review later. I will say, though, based on what I've read so far, that it doesn't just present a very well-done megadungeon level but that, even more impressively, also a very well-done fantasy setting. There are a lot of superb ideas in this module, some of which eerily parallel things I've been doing in my Dwimmermount campaign and that I've never revealed, even to my players. Whether this is a case of great minds thinking alike or fools never differing, I'll leave to others to decide.
Regardless, this is a fun product and well worth your purchase. More on it later.