Into the Underworld is a series of adventures released to support Season 2 Organized Play with 13th Age. The adventures were released to 13th Age Alliance GMs (a subscription service).
Each adventure is intended to take (about) two four-hour sessions to complete, "taking PCs into the realms below the Dragon Empire to investigate a fallen meteorite. But first they must face new enemies, as well as some familiar foes with new twists. Along the way they will encounter gods, strange subterranean seas, and the ever-present threat from the Star-Masks."