I have posted links below. The construction of this Vishnu temple apparently transcends human memory, yet it is a living, breathing place of worship today. Legends say it was built around the beginning of Kali Yuga, which would make it at least 5,000 years old, built around 3,200 BCE. There are documents from 300 CE that aver that this temple has been around for thousands of years. Lore and legends surround it, wrap it like the sculptures that encase it.
The Govt. of India recently did a study and opened 5 of the 6 secret vaults in it due to a court order. They found an astounding $22 Billion worth of gold and diamonds from all over the world, from ancient Greece and Rome to Japan, valued at "face value," antiques thousands of years old, without considering their antique value.
But, there is more. There is a door in the temple, the 6th vault, that cannot be opened. No physical locks hold them in place, yet the massive stone doors will not move. Legend says that only certain Vedic chants pronounced with perfection can open the doors safely, and any forced entry will be the trigger of enormous calamity. Some people have apparently died from undetermined causes, trying to force this decision in courts. No one wants to take that kind of risk. Links below.