Gulliver's Travels by Jonathan Swift
Gulliver is a ship's doctor. The book covers 16 years of his adventures at sea. He has gone to the end of the earth and keeps finding strange new countries. There's Lilliput where the people are six inches tall. Next is Brobdignag, where the inhabitants are giants. He finds the flying city of Laputa. And finally the country of Houyhnhnms which is run by a race of intelligent horses who are served by the savage humanoid Yahoos.
Swift writes a satire that covers religion, politics and human nature. It's amusing and thought provoking at the same time. And it was banned. It is critical of the politics of the time. It also critical of the different religions. It was considered wicked and obscene.