6. Steinway Tunnel
Underneath Grand Central used to be a trolley loop built in the 1890s under the direction of William Steinway, owner of the piano company which still exists in Astoria, Queens. The tunnels made only a handful of trips in the early 1900s before the tracks were sold to the city, and a large part has been left abandoned.
After the death of William Steinway, August Belmont, the founder of the Belmont Stakes, took the lead on the tunnel project. This came after an accidental explosion in December 1882 that killed five workers, as well as the disastrous Panic of 1893. Because the trolley enterprise was entirely privately run, Belmont was never granted a franchise to operate the line, leading him to sell the tunnels to the city. The tunnels were converted to rapid transit tunnels, and they were expanded after the rapid transit cars had difficulty making tight turns. One segment of the loop was later repurposed as a pump room.