Scenic prompts - talk about the underground

[charisstoma]

The site says: This massive network of underground tunnels dates all the way back to the Stone Age.
http://guiltyfix.com/wp-content/uploads/sites/2/2015/11/be0527ae-89a7-48a7-8d06-0b2bab7d48a6.jpg

Anyone with an idea where this set of images comes from?