Having fallen from public notice, the tunnel was rediscovered in 1981 by then 18-year-old Robert "Bob" Diamond, who entered from a manhole he located at Atlantic Avenue and Court Street, crawled a distance of 70 feet (21 m) underground through a filled-in section of tunnel less than two feet high, and located the bulkhead wall that sealed off the main portion of the tunnel. With the assistance of a Brooklyn Union Gas Co. (now National Grid) engineering crew, he then broke through the massive concrete bulkhead wall, which is several feet thick. Diamond thereby opened access to the main portion of the tunnel, and began to popularize the tunnel as an antiquity. He led tours of its interior through December 17, 2010. The tunnel has been listed on the National Register of Historic Places since 1989.
The History Channel series Cities of the Underworld ran a segment ("New York's Secret Societies") on the tunnel in Fall 2008. The TV show Treasure Hunters used it in an episode.
Read more about this topic: Cobble Hill Tunnel