So this is out in the wild, will not say exactly where as I don't want to see this griefed. Anyways I stumbled upon this and wondered if it is naturally occurring? I know that aside from the nether rack and fires that it could be. I also found a survival island that a group of people call home with a nether portal from where they got the nether rack and what not.
No someone has done this and I actually think I may know who so I will ask them to be sure but I can tell ya its man made...