This is a quest for drows only.
Go to the Underdark to do this quest. From the Drow Guardians, go n, ne, nw, 2n, nw, stairs, 2nw, 2n, w, sw, 2w, search wall, n, ne, e, n, ne, e, 2d, get gem.
After getting the gem, go back to the Drow Guardians once again. If you go north and north-east, there are two monsters. From there, enter darkness, s, 2e, ne, 2n, nw, 4ne, n, nw, n, hole. Once you've entered the hole, you will fight alot of spiders and other monsters here. What you need to do is to get 4 different kinds of gems from 4 certain monsters that exist here, which exist on 4 different locations.
Zaluth: Carrying a Blue Gem.
Aryxx'zath: Carrying a Purple Gem.
Sythri: Carrying a Black Gem.
Vrock: Carrying a Red Gem.
Once you've got those 4 gems, go find a Sacrificial Altar, and you'll find a spider there. Kill the spider, and 'sacrifice corpse to lolth' and go north. Now, you will be found on a bridge. Commands you can use here are 'pull handle', crank whell left/right' and after using go forward/back. There is a place where you will find Onyx Altar. There, you need to put the 4 gems in that altar, which gives you the message to go to the other side of the bridge. Get there, and kneel in front of the altar you'll find there. Now after doing this, you'll have to find your way back to get another 4 gems again to 'put gems in altar' once again to get the title. After doing this, get to the location where Yochlol is with the Blood Stone, and type 'enter portal' to leave.
What you also can do is during this time, is to find the location where Yochlol with the Blood Stone is. There is a hidden room close to him where a Demon Spider is. Kill the Demon Spider and take the Iron Horn of Valhalla. Go back to the bridge and give it to the Drow High Priestess that can be found in a different location. When trying to return to the bridge, there a a certain room in these two location where you need to 'pull lever'. I'm not sure if this thing with the Iron Horn of Valhalla is a part of the quest or something else.