Kaid Benfield writes at NRDC Switchboard that Helsinki is building an underground city to avoid urban sprawl. CNN's Richard Quest, " whose effusive reporting style may be to infrastructure what Dick Vitale's is to basketball," explains in a short video tour.
It is pretty wild, including industry, a giant cold storage facility, swimming pools and a central heating and cooling system. Given the climate, and how dark it is for half the year, hiding underground makes some sense. See it at Switchboard.