Originally built for Expo '70, this underground construction by architect Cesar Pelli now houses Japan's fourth national museum. The building – like a submarine, with walls over 3m thick and light filtering down through skylights above the lobby – is interesting, and there's a decent, if not mind-blowing, collection of 20th-century works by Japanese and international artists. The entrance is marked by a large sculpture of steel tubes, said to resemble a butterfly. There's discounted admission Friday and Saturday nights (adult/student ¥250/70).
The museum is located towards the western end of Naka-no-shima.