A couple of weeks ago I read a story called "Old Hundredth," by Brian Aldiss. Sometimes a story kind of stuns me with its imagination. This story is amazing.

Distant future on earth, after the moon left its orbit and fell into a close orbit around the sun. The earth and Venus became twinned an circle each other. Mankind colonized Venus, where we began populating the planet with genetic experiments. The scientists especially liked tinkering with extinct prehistoric mammals, and the main character of the short story is the product of such an experiment--a megatherium, a ground sloth that was as big as an elephant. But they gave this breed opposable thumbs and larger brains, and the MC has been traveling the world studying musicolumns. They activate when a sentient being comes near and play death songs left by others. The MC is going home to die and thinking of what song she'll leave behind. Hasn't been home in 300 years, because the large herbivores have to keep on the move to feed themselves. And so on and so on. Amazing stuff. Some stories...you wonder how that kind of thinking comes together, and you're glad it did.