I don't know if the bottom of the well counts, but I despise that place with all my fiber. It is so unspeakably evil, that it should be nuked. The walls are made of skulls, the music sounds like a woman being tortured, and every creature in there is the stuff of nightmares.
Next is the Shadow Temple for the same reasons. I hate the evilness that resides in there. Mainly because I hate redeads.
The City in the Sky. Seriously, it was such a boring temple. For a "city" it could've had a lot more to it, but I guess its emptiness went well with the abandoned theme it was trying to portray. Still, I was really bored throughout the whole temple and I still hate it.