This is an idea I had a pyramid which once discovered and explored would turn out to be spacecraft. I never played SpellJammer but always thought the idea was good or potential for a lot of fun.
The idea here would be a pyramid, I picture it more Mayan, than Egyptian, probably found in a jungle. It would be full of monsters of some sort, maybe a nest of a giant wasps, Octorillas, or Yuan Ti. After clearing the place out characters would find two stone thrones one on the top floor and another inside floor 2. They would also discover a Helmet of strange origin in a room on a lower level. Wearing the helmet and sitting in a throne would allow them to launch the craft into the AetherSphere.
I picture a secret room (8) that might contain a power source which might also be the phylactery of a Lich. Which could add complications. The magic helmet would be sentient and possible have it’s own motivations for flying the craft.
Travel through space would be fraught with peril. I imagine the the characters having to setup residence in the pyramid during flight, and space born creatures invading the ship from the outside during flight.