I recently got a chance to play around in an early build of Ark's second expansion, Aberration, which takes place in a series of underground biomes and introduces new movement systems like wingsuit gliding, rock-climbing, and ziplines. Originally planned for an October release, Studio Wildcard has announced that Aberration will now arrive on December 12.
Along with the new environments, and the new tools to get around in them, Aberration will of course arrive with new dinosaurs (or are they aliens?) such as the Rock Drake, which can glide, stick to walls, and become nearly invisible. There's also a hideous queen monster that can lay eggs inside you, causing you to give a rather messy chest-birth to a squirming worm grub. Gross! But fun.
The Aberration expansion will be priced at $20, and can also be purchased as part of the Ark season pass, which includes Scorched Earth and an as-yet unspecified third expansion. Ark itself is currently 50% off in the Steam store.