They have been determined to be more than 2000 years old and their construction is not recorded in any historical documents.

Although near each other, uniform in construction and design, and apparently made for the same unknown purpose, the caves have no cross-connecting passages, even though excavating a small tunnel would have required very little effort compared to the task undertaken to excavate any one cave.

my theory? ancient secret base for either some rich person or some government. or maybe religious or artistic in nature, given the ornamental wall carvings and aesthetic design

I wonder how long it took to dig all of that by hand. that's nuts.