The Temple

Summary
The temple-like structure that the Prophet of Regret occupied during his brief stay on Installation 05 was located in the center of a massive lake. The only way to way the temple without a dropship or aircraft was by taking a route through a series of underwater tunnles, over bridges, and by travelling on anti-gravity gondolas. The purpose of the temple-structure was never discovered because it was destroyed by a Covenant Battle Cruiser shortly after the Master Chief disposed of the Prophet of Regret.