Very much what it says on the tin - a mammoth complex all ready for you to populate with monsters, traps, loot and anything else which takes your fancy.
There's a one-page overview to show you how it should be laid out (along with a note that if you want to expand it, the publisher also has a 'desert tiles' set available), and then there are 20 sheets of tiles in an appropriate size to use with miniatures or tokens.
The grid pattern is nicely presented as actual tiles... as in a tiled floor. There are tonal variations so it isn't too boring, along with a few tiles of completely different colour and some with symbols on them. You'll have to decide their significance... or lack thereof.
If you like a good 'crawl but don't have the skills, time or inclination to map it, this should start you off. If you are really time-strapped, there are random 'dungeon contents' products available as well (try the Raging Swan Press "Dungeon Dressing" series, Ennead Games or Lee's Lists - all available here - for a start).