Space boffins believe they may be on the verge of discovering a vast, hidden network of tunnels beneath the surface of the Moon.
The tunnels aren't thought to be the work of long-extinct (or perhaps still surviving) intelligent moon aliens, perhaps driven to adopt a subterranean existence by a notional disappearing atmosphere aeons ago. Nor is any involvement by Tibetans, Elvis or others seeking a secluded dwelling far from prying human eyes suspected.
Instead, top moonologists think that they may be on the track of "lava tubes" not dissimilar to those of Earth. A lava tube, unsurprisingly, is a tube in solid surrounding rock along which at some point liquid lava has flowed (or is still flowing, in some Earthly cases).