The SeerAfter you finish your plot business at the Pharos, you'll be able to use the elevator at the first floor to reach an area called the Penumbra. In the four corners of this area are four pedestals into which you must deposit a number of Black Orbs, which are acquired by fighting the monsters that lurk in the walls.

Once you've lit all four pedestals, the elevator will admit you to a deeper area, called the Umbra. You must repeat the same business here, although the pedestals now require more Black Orbs. After that, you'll be able to reach the third area, the Abyssal, whose pedestals require yet larger amounts.

Once you're finished in the Abyssal, and if you were able to find and destroy the hidden boss in the Penumbra, you'll finally be given elevator access to the final area, "Unknown," which is nothing more than an arena for you to fight the Seer.