When a public transit system must find new revenue, innovation follows. In China, subway operators are answering the call with a radical solution: transforming stations from simple transit points into vibrant, multi-purpose commercial hubs. This nationwide facelift is redefining the very purpose of urban infrastructure, turning subterranean spaces into the heart of community and commerce. / The invisible threat of third-hand smoke (13:39). On the show: Steve, Niu Honglin & Yushan