While To Your Scattered Bodies Go is the more original of the two, The Fabulous Riverboat is in almost every other way a better book -- suspenseful, fast-moving, and full of true SF sense-of-wonder. Check out this marvelous series. "Resurrected on the lush, mysterious banks of Riverworld, along with the rest of humanity, Samuel Langhorne Clemens (a.k.a. Mark Twain) has a dream: to build a riverboat that will rival the most magnificent paddle-wheelers ever navigated on the mighty Mississippi. Then, to steer it up the endless waterway that dominates his new home planet -- and at last discover its hidden source. But before he can carry out his plan, he first must undertake a dangerous voyage to unearth a fallen meteor. This mission would require striking an uneasy alliance with the bloodthirsty Viking Erik Bloodaxe, treacherous King John of England, legendary French swordsman Cyrano de Bergerac, Greek adventurer Odysseus, and the infamous Nazi Hermann Göring. All for the purpose of storming the ominous stone tower at the mouth of the river, where the all-powerful overseers of Riverworld -- and their secrets -- lie in wait."

"Years have passed on Riverworld. Entire nations have risen, and savage wars have been fought -- all since the dead of Earth found themselves resurrected in their magnificent new homeworld. Yet the truth about the Ethicals, the powerful engineers of this mysterious "afterlife," remains unknown. But a curious cross-section of humanity is determined to change that situation... at any cost. Intrepid explorer Sir Richard Francis Burton leads the most remarkable voyage of discovery he has ever undertaken. Hot on his heels are Samuel Clemens, King John of England, and Cyrano de Bergerac. Spurred by the promise of ultimate answers, they chart a course across the vast polar sea--and toward the awesome tower that looms above it. But getting there will be more than half the battle. For death on Riverworld has become chillingly final..."

Final volume in the Riverworld series -- unless you want to count the assorted sequels Riverworld War (1980), The Gods of Riverworld (1983), or River of Eternity (1983). "The answers behind the enigmatic origins of Riverworld lie at last within reach, as the remarkable gathering of Earthlings -- including Sir Richard Francis Burton, Samuel Clemens, Alice Liddell Hargreaves, Cyrano de Bergerac, Ulysses S. Grant, and Baron Von Richtoven -- finally breaches the stronghold of Riverworld's extraordinary super-race. But answers would lead to more enigmatic questions... Who is the Mysterious Stranger who taunted the Riverworld resurrectees with hints of the truth? What is the key to the gargantuan computer that wields the power of life and death? The astonishing secrets lie within the Dark Tower -- but only for those brave enough to seek them and wise enough to decipher them..." "Charts a territory somewhere between Gulliver's Travels and Lord of the Rings" -- Time.