Imagine a vast technological leviathan...miles long, hundreds of stories high, home to hundreds of thousands of people...a trading vessel that plunges through the astral plane with an arcane space fold drive capable of piercing the astral plane.
But millennia ago, this ship became trapped in Astral space, unable to return to physical reality for some reason. Perhaps an erratic astral jump caused it to intersect with another ship, perhaps the warp drive bent space too far and it paradoxically destroyed itself.
Now it exists as a forgotten hulk on the edge of the imagination, an astral El Dorado filled with amazing treasures from a near forgotten golden age in the distant past. While there may be hidden treasures within the ship, there are also horrors, monsters and stranger things best left forgotten...things that will inevitably be faced by those who seek fame and fortune at the heart of the hulk.
What sorts of chambers might have existed on such a ship?
This variant on a megadungeon might be the next project once "Other Strangeness" has been completed.