Not sure if there's a more appropriate place to start this thread, but I found a link to a set of pictures taken from the subway system in Stockholm.
According to the post, some of the stations are carved from rock and were left with cave-like ceilings. I'm curious what some of the professionals in Cyburbia think about the design, set up, implied construction and operation costs, or just general impressions. Does anyone think something like this is feasible in the States? Are there any other really cool subway systems out there?