Any Ringworld fans out there? This story reminds me of Seeker.
For those who never read the book by Larry Niven, Ringworld is a structure with a circumference approximately equal to the earth’s orbit around the sun, and a width of a million miles. When landed on Ringworld, the horizon is flat, but appears to have an arch which disappears into the sun. Seeker is a character who is on an adventure to find the base of an arch. He has an extended lifespan, and has been walking for hundreds of years. The main characters don’t have the heart to tell him the truth.
