In the original game, the heroes were cave explorers trying to survive underground dangers such as poisonous gases, floods, and invisible monsters. This time, a new team of characters sets out to explore a volcano in search of a religious artifact. They have to reach the temple inside the volcano, face the temple guardians, then rush to get out before they are consumed by lava. On each round, players flip tiles to reveal paths, and select and perform a number of actions. Rolling the hazard die may spawn guardians, and when the eruption marker on the volcano track hits zero, it means it's time to run.
JW and me played Sub Terra in the One Player Guild meeting at this year's UKGE. My character inhaled noxious gases twice, which meant I had to wait for several rounds doing nothing, until another character arrived to revive me. This pretty much felt like player elimination. JW's character was a bouncer. He never had to protect anyone, and just strolled around the cave like a carefree spelunker. Perhaps these issues won't arise in the new version, though.
The Kickstarter campaign also offers two expansions (Arima's Light and Typhaon Wakes), as well as upgrade packs with minis instead of wooden meeples.