Sanctuary Fortress features a lot of electronic instruments that imitate the sound of repetitive beeping at various pitches, giving off a strong "technological" vibe to the song that fits the high-tech aesthetics of the fortress. The bass and percussion rhythms also evoke the traditional desert music style of other Echoes songs such as Luminoth Temple. The melody is performed by a choir or by a high-pitched synth, both of which give this song a much more upbeat and hopeful vibe compared to much of the Echoes soundtrack.
It is also one of the unlockable songs in the ingame Multiplayer, unlocked when Samus restores the Energy Controller of the Sanctuary Fortress and reports back to U-Mos. In Metroid Prime Trilogy, the song is available in the Soundtrack Gallery, costing one Silver Credit.
The later portions of the Fortress play an alternate version of this theme.
The main theme can be heard here: