After you have done the Sepulchre go to the bit with the gongs and the submerged bridge on the level called Miridans Pass.
First of all hit these gongs in order with Sangaril's Crossbow : Red, Yellow, and Blue.
Then when the bridge has extended: Orange, Green, Yellow, and Red.
Then when the next one extends: Blue, Orange, Red, Yellow, and Green.
Then walk across and you get 15,000 exp (I think) and a summoner ring.
I leveled up Sangaril, Taurgis and Maia 3 levels each here!