This is a floating ocean supply station for small boats and submarines. It's got fuel tanks for refueling and solar panels to generate power. Plus, there's a living area underwater where you can chill out and take a break. Oh, and there are even some windows in the living space to see inside the sea! The size is roughly 16 blocks square, and you can use an avatar to enter the station from above or within.
[Youtube movie]
https://youtu.be/jRhoLIsgd4I
