First Men in the Moon (1964)

Around the turn of the 20th century, Joseph Cavor (Lionel Jeffries), a brilliant British scientist, creates his own spacecraft and takes a trip to the moon, accompanied by explorers Arnold Bedford (Edward Judd) and Kate Callender (Martha Hyer). After landing, they encounter an insect-like alien race that lives under the moon's surface, which has an air-like atmosphere. After glimpsing the extraterrestrial society, the group must soon escape back to Earth.