So I am currently on a boat, going towards a distant continent. And I came across this...thing. I saw no other buildings or signs of life. Any ideas on why this was there?
Nope, someone simply built a portal in the nether, and MC saw there was an ocean where it needed to place the portal so it makes it hovering in the air. MC essentially makes a 18 obsidian block nether portal if its floating in the air.