They are often spartan in terms of decor, but lavish in terms of space. Take DC's metro as an example. The stations are mostly raw concrete, but they are massi

They are often spartan in terms of decor, but lavish in terms of space. Take DC's metro as an example. The stations are mostly raw concrete, but they are massive. The underground stations are cavernous vaults with sprawling mezzanines. The decor undoubtedly adds a bit to the cost, but it is nothing close to the cost of excavating two or three times as much space.