Here is a good place to start digging, I found an old post on R-ddit, asking about tunnels under Lexington: "I was skimming a History of Lexington, published in 1872, and came across some weird stuff. I was particularly curious about the claims of tunnels and caverns beneath the city.
The author G. W. Ranck described a gallery of tunnels somewhere beneath Lexington. The report detailed how, in 1776, hunters from the frontier town of Booneborough found rocks of “peculiar workmanship,” behind which was found a tunnel. The small opening inclined sharply into the rock and enlarged to a grand gallery about four feet wide and seven feet high. After a few hundred feet the gallery led to an even larger chamber that was 18 feet high, 100 feet wide and 300 feet in length. Inside of this chamber were found an altar, idols, and about 2,000 human mummies…."
Link to History of Lexington text : http://www.archive.org/stream/cu31924028845993/cu31924028845993_djvu.txt