The First Men in the Moon by H. G. Wells
Published exactly 100 years ago, this is one of Wells's greatest novels, and the only one of his scientific romances to embrace space travel. Thanks to the discovery of an anti-gravity metal, Cavorite, two Victorian Englishmen travel to the Moon, where they encounter the extraordinary underground world of the Selenites, insect-like aliens living in a rigidly organised hive society.