Exploring active and abandoned subway and underground railway tunnels, bores and stations is often considered to be trespassing and can result in civil prosecution. As a result, this type of exploration is rarely publicized. One important exception to this is the abandoned subway of Rochester, NY, the only American city to have an abandoned, formerly used, subway system. (The Cincinnati subway is also abandoned but was never completed.)

"take nothing but photographs,
leave nothing but footprints"