When you first enter this area you'll find yourself in a large open room with passages leading off to each side. These passages lead to graveyards. To the south of both graveyards is a water reservoir, but the one to the south has some toadstools lying on the ground next to it.
Passages leading from each graveyard to the north lead to rooms with two chests in each of them, and heading north from these rooms leads to a battle with Troglos and some Hulking Worgs.
Depending on which side you went up first going either south or north leads to another large room, except that this one contains more Troglos and Hulking Wopgs and two living statues.
Once you've cleared this level of enemies go into the small cubby to the northwest of the most second large room. There's a slith statue in here, and it's holding a Fine Slith Spear which you can take if you so desire. Now go back into the southern passageway, past the room with the chests and you should find a door leading into a small storage area. There's some Gremlin Wine in here which you can take if you want it.
Now go back to the northern central room and up one of the sets of stairs to the main Troglo Altar. There's a large group of Troglos and Hulking Worgs in here that you'll have to clear out. There are two magic rings in here, but I can't remember exactly where. The Magnetic Ring and the Resistance Ring. Make sure not to equip the Magnetic Ring, because it's cursed and will make you 50% more susceptible to being hit in combat.
There's two passages leading to the north, one to a dining hall and cellar, and the other to the storage room where the Troglos keep their robes and candles and such for ceremonies.
The one passageway leading to the south ends in a hallway with doors leading both east and west. The eastern doors lead to a common area and a Troglo Shaman. There's another door leading east from this room, but the spellbook just explodes, so you probably don't want to read it. The doors leading to the west are apparently where the Troglos sleep while they are there.
Now go back to the central area and up the steps to the Altar itself. You need to be standing right next to the Altar for the Ritual of Sanctification to work. When you try to approach you'll get a message to either Leave or Kneel. Choose Leave and you should then be right next to the Altar. Perform the ritual, but be aware that doing so will cause the appearance of Demons and Imps at each of the four corners of the platform.
Once you've gotten rid of the Demons and Imps leave the Altar and return to Shamirik. First go and tell Commander Corrie you've completed her quest, then go talk to Mayor Knight. he'll finally send you on your quest to speak to King Vothkaro. Castle Troglo can be found slightly northeast of Aminro.