The story starts with a man getting into a coffin size rocket and launching into outer space with no provisions. He lands on a planet of water with floating islands. The islands all have different forms of vegetation and animals on each one. There is one stationary island with transdimensional Adam and Eve type deities.
This is Perelandra, the second of Space Trilogy by C.S. Lewis.
(also titled Voyage to Venus in a later edition published by Pan Books) is the second book in the Space Trilogy of C. S. Lewis, set in the Field of Arbol. It was first published in 1943.