The Time Machine is a novella by H.G. Wells (free at Feedbooks) which is basically the birth of the idea of a machine which allows one to travel through time. Now that’s innovative.
Anyway the “Time Traveller” goes to the year 802,701 and finds the human race, or its descendants rather, in a state of deterioration. After having solved all of man’s problems with science, there is no more spirit of endurance or hard work, or anything that really makes man what it is. He eventually discovers that humans evolved into two sets of creatures, the Eloi and the Morlocks, who are different but also both no longer quite human. He spends quite a bit of time trying to recover the time machine as well since it disappears from where he had “landed”. Obviously we know he lived to tell the tale because well, he’s telling the tale. But no more spoilers! Read it and understand the roots of basically all time travel literature!