Sanctuary

Sanctury is the hidden bunker of the Covenant

Billions of years ago, Primus created the hive-like Sanctuary hidden deep below the deadly Protos to hide the Covenant. He filled with with miraculous machines, which the Covenant strives (has striven?) to improove over the ages.

Parts of Sanctuary

The Reflectorium

A completely mirrored meditative chamber, used for self-examination. You must pass through the Reflectorium after decontamination when entering Sanctuary.

The Stentorium

From Teletraan I: The Transformers Wiki, a Wikia wiki.