The Green Odyssey by Philip Jose Farmer

Alan Green is a space traveler stranded on a barbaric planet who has been taken slave and made a consort to an insipid and smelly queen. His slave-wife, though beautiful and smart, nags him constantly. He’s given up hope of ever returning to Earth when he hears of two astronauts who have been captured in a kingdom on the other side of the planet, and sets out on an action-packed journey on a ship sailing across vast grasslands on rolling pin-like wheels in a desperate scheme to save them and return home. Due to the non-renewal of its copyright, this book is in the public domain.