This is a post-apocalyptic story I think I read in Analog Magazine. I can't recall the title.
Illustrated on the first and second page of the story, showing an airship with a ladder let down, and people standing in front of an enormous cube.
The plot was that there was a/the Godsoul comet that [almost?] collided with earth. Most of civilization was wiped out and most of the world's land flooded. Their spirits (called piquinoes by the Liberians and worshiped as ancestors) are still around. The protagonist lives in Liberia, and he and a crew mount an expedition in a zepplin-like craft to visit the city of Denver. They find nothing except a white cube enclosing most of the remains of the city. They get inside and have have to deal with the Grey Men, who are the result of using a teleportation system to deal with the racial crisis. They have also produced the spirits as a byproduct.
Eventually, a member of their party uses the teleportation system to turn Jupiter into a new sun by making a connection to an antimatter universe.
The protagonist has been caught in the transport system. The backlash also destroys the new cube city and his body. He returns to Liberia and makes plans to revitalize society as a piquino.