After opening the gate, Mendoza will send you to search the inner part of the temple. Before you step below the large block, use telekinesis on the lever in the distance. The happy team will move further and you will end the task. Take a look at the next two stone pillars that you find.
Open the large drawbridge
Together with the Inquisitor, you reach a conclusion that the bridge needs to be lowered. Take the corridor on the right and go to another bridge. Use spells or a distance weapon to move the windlass on the other side. Deeper into the temple, you will find Brent. Complete The search for the map quest.
You can take a look around the caves. The corridor that's going down will lead you to Saurian buildings. In one of them you will find an anti-magic crystal, the other hold a big amount of magic scrolls. Return to Mendoza and show him the map. After reaching the small room with the Inquisitor, you will be sent to Vince (The opening to the crypt).
When you ask Mendoza about what needs to be done, he will lead you to a room with a pedestal on which you have to place the old bust received from the Inquisitor. Fight your way through the enemies, reach a stone pillar and examine it. Return to Vince. Have a word with the digging man and the Inquisitor and you can go inside the fortress through the hole in the wall, using the nautilus transformation scroll.