From Halopedia, the Halo wiki
Alien Corridors is the fifteenth track in Halo: Original Soundtrack.
The piece starts off with the "alien chimes" alone, but at 00:09, an extremely high synth note begins to assert itself, giving shape and pattern to the chimes. Starting at 00:19, a series of drums start up, giving the piece a driving, yet irregular, beat. At 00:31, a crash of cymbals leads the piece into its main section, allowing the drumbeats to push the piece into a slightly frenetic pace as the high-pitched synth fades out.
At 00:40, an even higher-pitched synth note takes over where the last one left off; the chimes shift their pattern and become somewhat more minor. At 00:49, another cymbal note removes the synth and sets the piece pace forward again as the chimes sound over the pulsing drums. At 00:56, the drums mostly drop out, revealing a midrange synth note underlying the piece; shortly thereafter, the high synth returns to give the beatless piece a sense of shape.
The piece continues without drums; at 01:17, the synth is joined by high strings, which slowly cycle through chords that drown out the chimes. At 01:29 the chimes become briefly audible again as the high strings fade out to make way for lower strings that continue the chords. The piece gradually fades out with the mid-range strings alone.
The piece was arranged into Xenoarchaeology in Halo: Combat Evolved Anniversary: Original Soundtrack.
The name of the piece alludes to the many narrow corridors onboard the Truth and Reconciliation.