I am looking for a story about a tiny universe smaller than our Solar System. It has one star and one planet, and the planet's orbit is on the edge of universe. The planet's single face points to its sun at all times. The world has a very tall wall around its twilight circumference.

A civilization grows on the planet. The ruler of the civilization - curious about what is beyond the wall - commissions for a ladder to be built up the wall. He climbs the ladder and walks towards the darkness beyond the twilight atop the wall. He keeps walking and

comes back to his original location. Anything that goes beyond the wall at the edge of the universe is reflected back on itself.

I think it starts with a quote like this: "Many and strange are the universes that exist like bubbles in the foam along the river of time."