Tunnel beneath the surface is thought to have been formed by volanoes.
A 50km long cave on the moon could be suited to harbouring a lunar base, according to Japanese scientists.
The feature was discovered by the orbiting Selene probe and confirmed by examining radiowaves beamed onto the surface.
The cave’s entrance is around 50 metres across but it widens to 100 metres in the interior. In some places it is as far as 200 metres under the surface.
Believed to have been caused by volcanic activity billions of years ago, the cave could be useful if humans seek to inhabit the moon because it could provide shelter from radioactivity and extreme temperature swings.
Temperatures on the surface of the moon can vary from more than 100°C to below minus 150°C.
Japan has said it wants to conduct a manned lunar mission by 2030.
