One of the common features of an epic is the "fabulous loci" for the hero to visit. Fantasy novels can have some loci that are quite pretty or terrifying, but science fiction has some that will make your jaw hit the floor. Try comparing the land of Fairie with a ring around a sun with a radius of an entire astronomical unit and a livable surface area of three million times Terra.
Some of them are even from reality, e.g., Saturn's Rings.
This entire page counts as backgrounds and plot ideas for science fiction authors.
A nice standard location is a famous mysterious lost spaceship, especially if it is full of treasure or something. This is commonly part of a treasure hunt story, with the protagonists searching for the ship in order to discover the Dread Secret of its disappearance. In many stories the lost spaceship also has the answer to some old mystery, typically something that the political powers that be would prefer to remain secret because it would shake things up. Examples include The Ghost Line: The Titanic of the Stars by Andrew Neil Gray, J.S. Herbison, All Cats Are Gray by Andre Norton, and A Talent for War by Jack McDevitt.
And in others it turns out that there is a blasted good reason the ship is lost, because there is Something Awful lurking inside. The protagonists who discover the ship are quick to regret it. Examples include Alien, Event Horizon, The Dark Side of the Moon, and ST:TOS Space Seed; which contain respectively the Xenomorph, a Gate To Hell, The Devil and Khan Noonien Singh.
If there are a huge number of lost spaceship, this turns into a Sargasso of Space.
If this is more a Mary Celeste situation (protagonists are not looking for a ship but unexpectedly encounter a recently deserted ship with hot food still on plates), it is called a Ghost Ship. Examples include Polaris by Jack McDevitt, ST:TOS The Tholian Web, The Black Hole, and 2010: Odyssey Two. In the movie Sunshine the Icarus I initially appears to be a Ghost Ship but it is actually a ship with Something Awful lurking inside.
If the ship has been traveling for centuries (sometimes containing a miserable crew that cannot escape), it is called a Flying Dutchman. Examples include Firebird by Jack McDevitt and Andromeda "The Mathematics of Tears".
In old pulp science fiction there is a long history of taking a dramatic and comfortable metaphor and transporting it intact into the outer space environment. Generally the author has to savagely pound a square peg into a round hole, with regrettable results. The classic horrible example is deep space fighter aircraft.
Most pulp falls for the old Space Is An Ocean fallacy along with the related misconceptions.
Many pulp writers figured they were the first to have the bright idea of transplating the colorful legend of the dreaded Sargasso Sea into science fiction. A deadly area of space that somehow traps spaceships who venture too close, only to join the deadly graveyard of lost ships. And not just human ships, a couple stories mention humans discovering wrecks of unknown alien spacecraft mixed in with the conventional ships. The graveyard typically contains everything from recent ships all the way back to historical ships dating to the dawn of space flight.
Some stories populate the graveyard of dead ships with castaways. Who will probably be interested in looting your ship of any supplies it contains.
The original legend dates back to when line-of-sight was limited to the horizon, so a sailing vessel poking at the edge of the sargasso could not see the interior. Not without being caught, that is.
With the invention of radar and the realization that there ain't no horizon in space, writers realized they'd have to make the space sargasso sea more invisible. Usually they'd add on the legend of the Bermuda Triangle in the form of an intermittent "hole in space" leading to a pocket universe. Some kind of wormhole or stargate that would transport the hapless spacecraft to a graveyard of lost ships safely out of sight.
Obviously this is highly unlikely to happen in the real world. But it sure is romantic, in a sci-fi pulp fiction sort of way.
When you are trying your hand at worldbuilding, please try to avoid ice planets, desert planets, swamp planets, farm planets, volcano planets, and other single-biome planets. The pejorative term for this mistake is Monocosm (term invented by Roz Kaveney). Jerry Pournelle parodied this trope with the phrase "It was raining on Mongo that morning"
The most famous is the planet Trantor from Isaac Asimov's Foundation trilogy (but given a much more detailed description in Donald Kingsbury's pastiche Psychohistorical Crisis). Trantor is famous among those literate in science fiction, the SF illiterates are familiar with the concept mostly from the planet Coruscant from the Star Wars series of movies.
There is a wide variety of life living in the free fall environment of the smoke ring, including a colony of humans. There are even aquatic creatures living in huge spherical floating ponds. (The Integral Trees, The Smoke Ring by Larry Niven)
Planets with no life are rather common (just look at our own solar system) and are rather boring. But nothing can beat the grim feeling of mortality engendered by examining a planet that used to have life. Especially if all the life died off rather abruptly.
A Forerunner planet is not too depressing if the culture basically died of old age. No more depressing than your average archeological dig. But if the entire planet still glows blue from an age-old nuclear armageddon, well, the explorers can't help but wonder if the political situation back home has taken a turn for the worse while they've been away.
How can planets die? Let me count the ways. The standard ways are:
- Nuclear War
- Gray Goo
- Stellar Pollution Shifting Habitable Zone
- Planetary Pollution
- Kessler Syndrome
- Total Planetary Destruction
...keeping in mind that most of these methods work equally well for a planetary civilization committing suicide or a planetary civilization exterminated by alien invaders. For more exotic apocalypses go here.
Well, maybe if you converted a Ringworld into a Bussard Ramjet to make a starship one astronomical unit in radius. That would be bigger.
Hang on, you could turn a star into a Shkadov thruster and turn an entire freaking solar system into a spaceship. Please pardon me, I have to go lie down a minute, my head hurts.
Please note that in our galaxy there are some real stars that are moving unusually fast.
Runaway stars are clipping along at around 100 kilometers per second. They are thought to be binary stars which passed too close to another star so one star got sling-shotted out. Or one star of a binary star system where the other blew up in a supernova. For science fictional purposes some sinister alien race converted their sun into a Shkadov thruster so they could go cruising for trouble.
A good example is Barnard's Star aka "Barnard's Runaway Star" or "Greyhound of the Skies". Astronomers measured the lateral speed and the radial velocity to calculate a space velocity of 142 km/s which is smokin'. And it is only 1.8 parsecs away (5.98 light-years), making it the fourth-closest star to the Sun. Jack Williamson used this in his novel The Legion of Space, home of the dreaded giant jellyfish-like Medusae who drive their solar system like a rocketship to invade innocent planets.
Hypervelocity stars on the other hand are screaming along like the proverbial bat-outta-hell. They move at about 1,000 km/s, which is quite a bit more than the galaxy's escape velocity. They are thought to have been sling-shotted by the Sagittarius A* supermassive black hole at the center of the galaxy. For science fictional purposes they are Shkadov thruster stars with the pedal to the metal, doing their best to get the heck outta Dodge ASAP. The important plot question being: what do they know that we don't? Apparently there is some awful thing that terrifies a civilization powerful enough to thrust their entire solar system up to a thousand klicks a second.