Marunouchi oazo gets its name from the Esperanto word for oasis. It was designed as a total relaxation complex, a "mental oasis" where people can escape the hustle and bustle of the city, and especially those who work in the busy business districts nearby. It's located just in front of Tokyo Station's Marunouchi North Exit.
Marunouchi oazo includes four interconnected buildings, the largest two of which have 29 floors above ground and four under. It has various public spaces where you can relax, as well as restaurants, coffee shops, a hotel, and various shops including the giant Maruzen Bookstore.