Haven’t seen this book mentioned
Against the Fall of Night
Arthur C. Clarke
STRANGER IN A STRANGE LAND
Dying Inside by Robert Silverberg
The Book of Skulls by Robert Silverberg
I could make a long list of great sci fi / fantasy. But these two IMO are quite readable as an adult at any age. More age durable in a manner of speaking.
A separate note. If you keep in mind that it was written in 1963 (relevant for several reasons), Glory Road by Robert A. Heinlein is a lot of fun. Sort of swashbuckling without the sex and profanity.
Ringworld, and Protector, both by Larry Niven..
I must add one most extra ordinary author since no one has mentioned him.
L. Sprague de Camp
Not possible to pick a “best” novel (you have to read his pedigree), but an historical fiction fantasy sci fi novel for any aged reader is “Lest Darkness Fall”. A 1939 publication that is not in the least dated. Seriously. You’ll see why.
For straight science fiction, Arthur C Clarke’s “A Fall of Moondust is one of my favorites, and I found his short-story “The Wind from the Sun to be most intriguing idea.
Farnhams Freehold by Heinlein was one of my favorites at the time.
The Andromeda Strain.
Childhood’s End (Clarke 1953)
Stranger in a Strange Land
My two favorites are by Dean Koontz:
Watchers 1987
Lightning 1988
Thank you for this thread!
You seek the impossible IMneverHO.
I could possibly narrow it down to 3 authors but that would miss sooooo much.
Here are a few so far unmentioned stories from mentioned authors.
Larry Niven “A World Out of Time”
Is his short story ‘Rammer’ made into a novel.
Also by Niven,
“The Long ARM of Gil Hamilton” and
“The Last Days of the Permanent Floating Riot Club”
My ficticious alter ego is a ‘Childless Protector’.
Robert A. Heinlein “Starman Jones”
Clifford D. Simak “The Big Front Yard”
This story can be found in the book ‘Over the River and Through the Woods’
Isaac Asimov “The Currents of Space”
As I age and reading becomes a challenge I have been collecting audiobooks. One good source of sci-fi stories is
https://librivox.org/
The best part of getting old and forgetfull is that I get to re-enjoy my favorites a second time as if they were new.
Sad/NOTsad but true.
Dune by Frank Herbert
The Dying Earth by Jack Vance
Book of The New Sun by Gene Wolfe
Freegards
Starship Troopers
Dune
The Forever War
Childhoods End
Martian Chronicles
Rendezvous With Rama
I’m surprised Gateway from Frederik Pohl hasn’t been mentioned so I’ll toss that one in.
Who doesn’t want to be Lazarus Long? So, Time Enough For Love.
Ring world is right up there, and I of course have to mention the World Of Tiers universe(s) by Philip José Farmer.
Back in the dark ages, a fanzine that I participated in (back when such things were done on paper and sent by mail) did an extensive project to rate SF books. Among books with at least 10 ratings, Lord of the Rings was the highest rated, and Watership Down was second. Not counting those as Science Fiction, the highest rated SF books were: More Than Human, A Canticle for Liebowitz, and The Stars My Destination.
My top rated were Rendezvous with Rama, The Moon is a Harsh Mistress, Foundation Trilogy, Cities in Flight, Way Station and Little Fuzzy (couldn’t stick to 3).
Lucifer’s Hammer, Ring World and Rendezvous With Rama.
Most of the books by C.J. Cherryh. Also enjoyed some books by Stirling. Never enjoyed books by Asimov.
Best SciFi Bump List! Thanks. ;-)