What Once was Lost
From Halopedia, the Halo wiki
<video name="What_Once_Was_Lost" width="200" align="right"/> What Once was Lost is a soundtrack piece included in the Halo: Original Soundtrack. It runs for 1:42 minutes.
Appearances
It plays during the outside portion of the level 343 Guilty Spark, and also during a portion of Keyes. It adds to the tension the player feels before and after discovering the Flood. It primarily uses swamp noises such as animal cries, with undertones to add to the suspense. The soundtrack itself creates much of tension to suit the dark mood of the level.