Those areas are both part of the "Cult of the Unseeing Eye" quest. Just pay a visit to the temple district, and walk around until you get an in game cut scene involving the cult in the streets. After the cutscene is over, you get an offer from the temple of Helm asking you to basically spy on this cult. Take them up on their offer, then enter the sewers within the temple district. When the time comes and you encounter the cult's head honcho, try and be friendly, he gives you the key to the door that descends into the rift area. The ghoul lord area is when you come back to the cult from the rift area. You have two options here: You can talk to the cult's head honcho again (he's in the south room) and trigger a fight, or you can go down the exit next to the room and "deliver" the artifact to the beholder yourself (this exit leads to the ghoul lord area). I recommend the latter, but it is not an easy fight unless you have either the Sheild of Balduran or the Cloak of Mirroring. If you have neither of these, you can just use alot of summoned critters to do your dirty work. Elementals and Invisible Stalkers are your best bet, along with a character in your party with invisibility to lead them to the bad guys.