Frankenstein has been called the first science fiction novel, but there are several other contenders for that title. For instance, you might try Utopia by Thomas More, the original work about a perfect land, and a book that has been even more influential than Frankenstein.
Or there's The Man in the Moone by Francis Godwin, about an anti-hero shipwrecked on a remote island, who tries to escape by building carriage powered by wild geese. But the geese, as it was then believed, migrated to the Moon, so he is swept along, experiencing weightlessness along the way, and then discovering a noble society on the moon.
Or, again, there's The Blazing World by Margaret Cavendish, in which a lady is kidnapped by pirates, abandoned at the North Pole, finds another world joined to ours at the pole, and in time becomes empress of that world.
Meanwhile, Frankenstein has inspired very many books as sequels or variations of the story. There is, for instance, Frankenstein Unbound by Brian Aldiss, in which a 21st century politician is transported back to Geneva in 1816 to meet both Mary Shelley and Victor Frankenstein.
Or there's Brittle Innings by Michael Bishop, in which the immortal creature survives the Arctic wastes and reappears in the Deep South of America during World War Two playing minor league baseball.