To Your Scattered Bodies Go (1971) by Philip Jose Farmer

Wikipedia wrote:To Your Scattered Bodies Go (1971) is a science fiction novel and the first book in the Riverworld series of books by Philip José Farmer. It won a Hugo Award for Best Novel in 1972 at the 30th Worldcon.

This was Farmer's most famous work and deservedly so - it was cloaked in ambition and revolved around a premise that made reading it a compulsory, nearly obsessive experience.

The premise is spectacular - all of humanity, all those who were born and died in the past 100,000 years or so and to the near future, is resurrected along the shore of a 20 million-mile river on an unknown world. This includes cavemen and even an alien named Monat. Almost everyone is restored in 25-year old bodies, bald and naked; the exceptions are those who died as children; these age until they are 25 years old and no one ages beyond that age. Those who died at less than 5 years of age, it is later revealed, have been resurrected elsewhere, on a planet called Gardenworld. The main character is the famous 19th-century British explorer Richard Burton (not to be confused with the actor).  He and a few others eventually make it their goal to reach the source of the river and perhaps find out who or what is behind this mass resurrection.

The people on this world are provided for - each has been supplied with a metallic cylinder which can retrieve food and supplies from large grailstones situated along the river every couple of miles.  Burton's group encounters the less civilized members of humanity, notably Hermann Goring, who had quickly managed to set up a minor kingdom with himself as the leading despot. Eventually, it is also discovered that anyone who dies on this world is automatically resurrected at a different, arbitrary location on the river's shore; hence, there is no longer the fear of death as on Earth. Burton eventually encounters the beings known as "Ethicals" - the ones responsible for this 2nd phase of humanity's existence.
This read very well, making the reader wonder what would happen next and what were the answers to all the mysteries, as well as being a cosmic supposition about mankind's destiny in this universe. Farmer tried to supply some answers in the sequel novels - The Fabulous Riverboat (71), The Dark Design (77), The Magic Labyrinth (80) and finally Gods of Riverworld (83).  There were also collections of short stories.  BoG's Score for 1st one: 8.5 out of 10

To Your Trivia Go: there were a couple of attempts to adapt this to TV, titled simply Riverworld, in 2003 and 2010; the 2003 SciFi Channel movie was planned to precede a TV series but nothing ever came of it, and it wrongly went with new different characters. The 2010 try was a longer 2-part TV movie, but both attempts failed to capture the wonder of Farmer's exercise.