ICYMI - Underground Tunnels of Philadelphia and NYC - Older articles with pictures. NYC and Central Park  https://gizmodo.com/an-artificial-cave-200-beneath-central-park-with-micha-1446538828 https://ny.curbed.com/maps/nyc-subway-secret-tunnels https://www.nycsubway.org/wiki/The_Steinway_Tunnels_(1960) Philadelphia https://hiddencityphila.org/2016/12/underground-concourse-revival-sees-light-of-day/ https://nextcity.org/daily/entry/philadelphia-septa-tunnels-walk-underground-septa-stations https://www.phillyvoice.com/exploring-urban-myth-jewelers-row-tunnels/ Great source for old tunnel maps -  https://www.nycsubway.org/wiki/Historical_Maps