This was once a temple used by Kuo-Toa - that's the structure at the south end of the map with the well in front of it in the rough cave. They also had the back exit. Later it was taken over by slavers, who built the double fortress fronting the main cavern, as well as the look-out tower that has since collapsed by the back entrance. Now, it depends on what you want it to be. In my campaign, it has just been put back together by another group of slavers, but they haven't found the two secret door, and have not bothered to move into the back entrance area.
(Hand drawn in pencil, parchment created entirely digitally. This was my first scanned map, so the grid was lost and I had to create a grid in photoshop to superimpose over the map)