I think what you may be thinking of near the Four Seasons is the large area of underground walkways in the area near the subway station to the west of the hotel in Marunouchi.

No, that's nothing - what I'm saying is that from the basement of the building your hotel is in, you can walk north and then west to upper Otemachi (maybe 20 minutes), or west and then south and then east to Higashi-Ginza (maybe 30 minutes). So a lot more than 1/2 mile, with underground connections to well over a hundred buildings.