To Sail Beyond the Sunset by Robert A Heinlein (Paperback) Ace Books, 1988.
To sail beyond the sunset was the last novel published before Heinlein died in 1988. It is the last of the "Lazarus Long" cycle of stories, involving time travel, parallel dimensions, free love, voluntary incest, and a concept that Heinlein named pantheistic solipsism -- the theory that universes are created by the act of imagining them so that somewhere (for example) the Land of Oz is real. It can easily be considered the capstone to the series, as it ends on a note very suggestive of an epic's finale.
By Robert A. Heinlein - Ace Books (1988) - Paperback -