Tephra Cave (テフラ洞窟) is a Field Track in Xenoblade Chronicles, composed and arranged by Manami Kiyota. It is track 6 of disc 3 from the Xenoblade Original Soundtrack. This music is heard while the party is inside Tephra Cave, though it does not play when the party reaches the outdoor portion at Kneecap Hill on the approach to the Bionis' Leg.
In Xenoblade Chronicles: Definitive Edition, this song also plays in the Time Attack hub, as well as in the Nerthis Necropolis in Future Connected.