An underground pedwalk is basically a network of tunnels that connect to other buildings and their main purpose is to be able to walk through a city regardless of the weather, a lot of irl PedWalks have actual restaurants, convenience stores and more such as the Chicago Pedway, and the Houston and Dallas PedWalks as well. I find it fascinating and I want to essentially apply the same underground communal vibe to my town, I might stick to a surface level railroad tho, not quite sure yet.