The Lunar Sea Spire is an abandoned temple that was once an oasis for Gems on Earth. It is currently at the bottom of the sea after Steven Universe failed to restore it in his first mission.
Description[]
The Lunar Sea Spire was a free-standing tower structure in the middle of the ocean. Each consecutive floor was slightly smaller than the one before. At the top, there was a shrine to the Moon Goddess. When the Moon Goddess Statue returns to the pedestal, it repairs any damage to the structure. Gems used to gather at the Spire, but, in current times, the Spire has been abandoned. The Spire possessed an extreme gravitational pull that kept the waves from sinking it.
History[]
My Little Universe: Mindwarp[]
As Steven Universe was traveling through the Dreamscape, he came across the Lunar Sea Spire, where a past Lapis Lazuli was currently working at along with a number of other Gems.
Season 4[]
When Steven finds the Moon Goddess Statue, he brings up the Lunar Sea Spire and how he failed to restore it on his first mission. It is also revealed by Pearl that it wasn't too important, as they made it as a test for him.