Chants of Sennaar

After you solve the puzzles of the Abbey and learn all 34 glyphs of the language (not exclusively necessary to progress, but is certainly suggested), you will uncover an underground area.  Make it through the dark maze of rooms with your newly lit torch to turn the water off and make your way to the other side of the gate guarded by the Warriors. Move up to the left of the screen and you will arrive at a set of tall white steps. The trophy should unlock here as you ascend to The Frontier level.

While in the underground area, be sure to check out The Preacher's fate  so you can knock that out.

Below is a full Walkthrough of all Abbey level puzzles, glyph cyphers and miscellanious trophies: