In the era of the internet it has become pretty easy to create things by creating a homepage about them. This happens all the time and for various reasons. For example, there is the Hommingberger Gepardenforelle, invented by an German computer journal. They created a mystical trout to check how search engines would list the term.
Inventing a cave by creating a website is pretty strange. Not many people are interested in caves, most like them as a movie location, if the scene does not take too long. Creating a cave hoax for explaining the source of faked archaeological treasures makes some sense. But a virtual cave, which is only funny for people knowing more about caves, is a sort of insider joke. Two examples we found on the web are from Great Britain, and we guess it is an example of the proverbial British Humour. A natural cave version of the Treacle Mines.
So no matter how good those websites look, the caves do not exist. Do not let them fool you!