Last time we discussed this, SDMB Denver claimed to have the oldest continuously operating district steam system in the world, including, last time they looked bits of original insulation made with hollowed-out logs. And NYC said the same kind of thing:
Steam also rises from manhole covers where waste-water is released from buildings. In my town you wouldn’t see that, because the sewer system is never vented that way, and is not run in a way that exposes sewer pipes to water infiltration, and it doesn’t get that cold anyway, but I understand that in some US cities traditionally some indigent people sleep over building outfalls in winter.