A subway system in an ancient city like Greece and Rome is always strange. When you ride them as an American, it seems like the strangest thing in the world to exit a subway and suddenly see something like the Coliseum facing you right out the exit.
Building them is even more mind boggling, as evidenced by the discovery of an ancient grave found while digging for a Greek subway. Imagine how many other random graves that old are still lying underground in these cities.