Undergrounds in Japan are awesome. In Tokyo, subway stations can be very huge, it's really a small town underground. You can easily be lost, searching for an exit. You walk, you walk, and when you go upstairs sometime you are directly in a building. It's very convenient when it's raining, you may go where you want without going outside !
Well said. Yes, several stations are like small cities and are easy to get lost in. There are parking structures underground all over the city too..