The Box of Many Things

Once you have unlocked the Box of Many Things by completing The Box of Many Things, it is available in the Torghast antechamber, next to the Wayfinder. in the Runecarver's Oubliette. It's on the left as you walk in the door.

The Box of Many Things is a researchable talent tree which gives you permanent buffs in Torghast. In order to research the talents, you spend Tower Knowledge.

You earn Tower Knowledge by completing Torghast runs, and you earn more TK the better your score is for that run. You get a higher score in Torghast for completing the run faster, killing everything, looting chests, saving souls, breaking urns, etc.

You can see how much TK you have when you open the Box of Many Things on the upper right of the pane. Or you can check your TK balance any time in game by looking at the Currency tab of your Character Info screen (click your portrait in the lower right of your WoW screen, or by default press C to open Character Info).