I have always been a science-fiction geek and so from this I was always interested in stories of alien encounters and secret government cover-ups such as project bluebook and Majestic-12.
One of the early books I read probably when I was about 12 or 13 was "The Gold of the Gods" by Erich von Daniken. In this book von Daniken describes being shown into a huge system of tunnels that extended out under the Pacific Ocean and that were filled with gold artefacts and a library that was written on a huge collection of metal discs. The books has photos of the entrance to the cave system and of some of the artefacts.
This is one of a series of books that develops his theme from "Chariots of the Gods" that the meso-american civilisations were exposed to Alien technology and that we have been visited by Aliens who we think of as Gods and that UFOs are their chariots.
So here is more evidence of these visitations because there is a level of technology that does not fit with what we know of meso-American history. The problem is that it does not exist. The poor archaeologist who showed him the site then had to explain to the authorities where all these artefacts had gone as they did not actually exist. He had made up the extent of the tunnel system and the library. This is an example of pseudo-science, the hijacking of scientific language and presentation to make something appear to be scientific while not actually following scientific method. You cannot always trust what you read or believe the photos that you see.
For a clear debunking of von Daniken's claims you should read Ronald Story's book The Space Gods Revealed. Sadly it looks like Story's book is out of print but von Daniken's frauds continue to sell well. As wikipedia would say knowledge is not democratic. Just because lots of people believe it, does not mean it is true.