I'm not gonna get my hopes up - One possibility is that it's simply some limited interior of a crashed or derelict alien ship, that is being looked at with vanity camera. (Similar to how people take closeups of destroyed shipwreck interiors)
Probably new surface structure, like any planetary base since horizon release, acting as a "cave".
The surface generation system can't create caves, so it needs to be hand made structure. Hopefully there is more game play there than with the other new structures they added in 2.3. We really don't need new skin for place were we can scan some beacons, pick up couple tons of some random cargo.