[moopogyOvenny]

Hmm it wasn't one of the early attempts at Riverworld by Phillip Jose Farmer, was it? The original Riverworld story was titled Owe for the Flesh and ended with the protagonist (called Richard Black in this version) finding the tower at the end of the river. Farmer entered a sci-fi contest run by Shasta Press and subsidized by Pocket Books, submitting his 150,000-word entry. He won the contest, but received no money. The work was never published and was lost in its original form. A later, revised manuscript (itself lost for decades) was discovered and published in 1983 as River of Eternity.