Science fiction novel or short story. Characters were lost or crashed or something on a new-to-them world and were making for a mountain they could see in the distance. But when they reached the mountain, it turned out to be a hole blasted by an asteroid through the "world" they were on, which turned out to be some kind of flat fake habitat floating in space.
37This happens in Ringworld. The mountain, “Fist of God” extends beyond the atmosphere. It plays a key role in the visitors’ escape– James McLeodJul 21, 2019 at 12:55
existing hub for duplicates at scifi.stackexchange.com/questions/94578/…– OtisJul 24, 2019 at 4:32
@Sprout you should probably take a look at the bounty and accepting the question...– Peter NielsenDec 12, 2021 at 21:47
Well, since Sprout has not been on the site in over 2 years and has only posted 1 question, I doubt he will be returning.– NJohnnyDec 13, 2021 at 8:47
This is almost definitely Ringworld by Larry Niven.
The mountain in question appears strange to Louis and company because it's so big, and it's located in the middle of the ring, while most of the mountains are part of the ringwall.
"That's the biggest tanj mountain I ever saw in my life."
He had spoken too softly. "A mountain!" he bellowed. "Wait'll you see it! The Ringworld engineers must have wanted to put one big mountain in the world, one mountain too big to use. Too big to grow coffee on, or trees, too big even for skiing. It's magnificent!"
It was magnificent. One mountain, roughly conical, all alone, forming no part of a chain. It had the look of a volcano, a mock-volcano, for beneath the Ringworld there was no magma to form volcanos. Its base was lost in mist. Its higher slopes showed clear through what must be thinning air, and its peak had a shiny look of snow: dirty snow, not bright enough to be clean snow. Perhaps permafrost.
There was a crystal clarity to the edges of the peak. Could it thrust clear out of the atmosphere? A real mountain that size would collapse of its own weight; but this mountain would be a mere shell of ring foundation material.
Louis realizes that what Fist-of-God (what the natives call the mountain) is, but refuses to say so aloud because he doesn't risk appearing foolish until the moment they reach the top.
"Remember the night you explored a giant map of the Ringworld? You couldn't find Fist-of-God. Why not?"
The kzin didn't answer.
"It wasn't there, that's why not. It wasn't there when the map was made."
"Louis, just what do you expect to find in Fist-of-God crater?"
"Stars," said Louis Wa.
The kzin was tense too. "Do not mock me! In all honor---"
---And they were through. There wasn't any pass. There was only a broken eggshell of Ringworld foundation material, stretched by terrific stresses to a few feet of thickness; and beyond that, the crater in Fist-of-God Mountain.
They were falling. And the crater was full of stars.
There appears to be a bit of confusion as to the structure; in brief Ringworld is a megastructure approximately 300 million km (300 Gm) in diameter (950 million km in circumference) and about 1.6 million km (1.6 Gm) in width. It is relatively thin, on the order of 10s of km thick, and rotates about its central star to produce around 1g of pseudogravity. Millennia before the story, a moon-sized interstellar rogue planetoid struck the outward-facing side of the ring at speed.
11That is IT! Thank you. I felt sheepish asking, because I knew it was going to be a novel very familiar to readers of Science Fiction, but it was completely escaping me. And now I am excited to re-read it! Thanks again!– SproutJul 21, 2019 at 14:08
21@Sprout No need to feel embarrassed; we've all forgotten things. Since this is correct you should click on the checkmark in the upper-left corner of the answer, just under the voting arrows; this will indicate to future searchers that the answer is correct.– DavidWJul 21, 2019 at 14:15
12@TeleportingGoat - It's a hole way at the top. Picture poking a hole through a plastic garbage bag - it stretches and stretches and finally pops through at the top. Fist-of-God is exactly that - a massive piece of space debris hitting the underside of the Ringworld, stretching the material upward, and finally piercing through above the height of the walls, so the atmosphere doesn't leak out. Jul 22, 2019 at 13:45
4@VBartilucci Ah, so it actually is a mountain, just an unintended one. From what was written above I (and apparently others) took it to mean it was just a big hole in the ground.– EborbobJul 22, 2019 at 13:51
3@Draco18s It is that way, because the defence systems protect against things falling onto the inside edge of the ringworld. A moon+ sized planetoid hitting the bottom was highly unlikely, and not handled by the "automated" defences.– YakkJul 23, 2019 at 14:17