What is this? An ear?

Take a look at a temporary art installation at New York City’s Rockefeller Center. A 30 foot pool towers over tourists for two months during the Spring of 2016.
Take a look at a temporary art installation at New York City’s Rockefeller Center. A 30 foot pool towers over tourists for two months during the Spring of 2016.
How a walk on a nature trail ignited a fire to step back in time. What are these tunnels? Why are they on the side of a mountain? What were they used for?