I'm currently in the middle of reading Journey into Space by Toby Litt, which is about a generation ship and includes some breathtakingly beautiful descriptions of meteorology and the Lake District.
And, like a perfect idiot, I went and started reading this review by Ursula Le Guin of the same, and of course, not many paragraphs in, ran into massive spoilers. So I'll go back and read that properly once I've finished the novel.
If you can't go faster that the speed of light and you're going somewhere far away, it's going to take more than a human lifetime to get there. People will have to be born (and die) on the same spaceship. Hence: generation ship. I like generation ships (and there are lots listed at that link). The concept raises some interesting issues: how do you maintain knowledge? Particular social values? Do people get bored? Does the 6th generation still care about landing? Do wars happens; do they care about Earth? Is it all just a metaphor for growing up and getting old?
Here are several more generation ship novels.
My favourite is Paradises Lost, a novella in Le Guin's collection Birthday of the World. Early on, she gets across the lack of danger (and variety) on-ship:
The smaller-order world revealed here is an austere one. No amoeba oozing along, or graceful paisley-paramecium, or vacuum-cleaning rotifer; no creature larger than bacteria, juddering endlessly under the impacts of molecules.
And only certain bacteria. No molds, no wild yeasts. No virus (down another order). Nothing that causes disease in human beings or in plants. Nothing but the necessary bacteria, the house-cleaners, the digesters, the makers of dirt -- clean dirt. There is no gangrene in the world, no blood poisoning. No colds in the head, no flu, no measles, no plague, no typhus or typhoid or tuberculosis or AIDS or dengue or cholera or yellow fever or ebola or syphilis or poliomyelitis or leprosy or bilharzia or herpes, no chickenpox, no cold sores, no shingles. No Lyme disease. No ticks. No malaria. No mosquitoes. No fleas or flies, no roaches or spiders, no weevils or worms. Nothing in the world has more or less than two legs. Nothing has wings. Nothing sucks blood. Nothing hides in tiny crevices, waves tendrils, scuttles into shadows, lays eggs, washes its fur, clicks its mandibles, or turns around three times before it lies down with its nose on its tail. Nothing has a tail. Nothing in the world has tentacles or fins or paws or claws. Nothing in the world soars. Nothing swims. Nothing purrs, barks, growls, roars, chitters, trills, or cries repeatedly two notes, a descending fourth, for three months of the year. There are no months of the year. There is no moon. There is no year. There is no sun. Time is divided into lightcycles, darkcycles, and and tendays. Every 365.25 cycles there is a celebration and a number called The Year is changed. This Year is 141. It says so on the schoolroom clock.