Formerly part of an integral water treatment system and a large retaining wall, this island has been long forgotten. The crumbling structures and rocky surface make it a very dangerous placer, and thus is a restricted area.

A small forerunner facility in a remote area, and like many other forerunner structures it's actual purpose is unknown. It's tight quarters make for intense combat situations.
The name comes from the top down view, which is actually the marathon symbol

Part of an intricate Underground Highway this area was sealed off due to several breaks in the rest of the highway. The large doors make entering and exiting the highway itself impossible. The interiors consist of several leisure areas, for the people who wish to take a break (much like gas stations, only way nicer. This has not been implemented yet). There is also an intricate maze of maintenance tunnels used by the workers, who have all abondoned the highway.

Just underneath the surface of Halo this large arena type area has no visible entrances or exits other than from the top, giving it the illusion of a prison. However the interior appears to have served some purpose, as there are grav lifts, teleporters and decorative walls all throughout the arena.

A small multi-level facility somewhere on Halo. Whatever purpose it may once have served will forever be a mystery, but the carnage that has taken place since is nothing if not legendary.