The Temple of Light is the only known place in the Sacred Realm in OoT. It's also the place where the Six Sages remain, where their powers increase.
Very little is known about the Temple of Light. Link only visits it six times. The best (and only) known place of this Temple is the Chamber of Sages. From this room, the Six Sages can gather their powers to seal the Evil King Ganondorf.
The Temple of Light is situated in the very centre of the Sacred Realm and the resting place of the Triforce. Its power seems great, since it can resist magically to Ganondorf's evil monsters, that have already conquered both Hyrule and the Sacred Realm. This Temple, presumably built with the power of Triforce, is controlled by its only known inhabitant, Rauru, the Sage of Light