Are there thousand mile long tunnells build by super technology and filled with gold ...cmon man

Technologically speaking its possible. The only difference between building numerous huge underground cities with interconnected maglevs, and building the NYC subway system is one of time and money., not technology. Also, if one had trillions of dollars of gold to hide, what better place is there?

Having said that, its impossible to corroborate, so for me its a maybe: a data point I store for future Declas.