Oh shit, I think it's Atlantis from Nadia Secret of Blue Water, just filtered to hell and back. This might seem a little farfetched but another image shows the Second Impact report with the history of Gainax as filler text, but also filtered to hell and with a different photo on the report.
I can't find any screenshots, and even if I could, this forum's UI is so ancient that I have no idea how I would even begin to embed it, but here's a link to the episode where they enter Atlantis https://youtu.be/y60_6sWFAS4?t=627
That skinny pyramid thing looks very similar to Atlantis' Tower of Babel, just without the inverted ziggurat on top. The surrounding area is the remains of the city, and the pit in the center is the mass grave, that angled line leading down into it from the top left being the path Nemo and his crew take in the episode in order to hold a funeral for their recently deceased crew members. Obviously this is very loose, but looking over all these other edits and speculative posts, I think this is just as valid.