The wall runs to two hundred and eighty-five metres. Art Tower Mito is a single institution containing three things — a concert hall, a theatre and a contemporary art gallery — and it opened in March 1990. The gallery has nine rooms, and the combined length of their hanging walls comes to 285 metres, which is the figure that actually describes what the building is able to do rather than how much ground it covers.

A tower a hundred metres high stands on the plaza, with the observation room at 86.4 metres, and it is visible from most of the central district. The design came from Arata Isozaki's atelier, and the problem it solved was holding three quite different uses on one site while giving them a common address: the plaza and the tower do that work. The building adjoins the Izumichō shopping street rather than standing in a park of its own, the station is about ten minutes away by bus, and Mito being a prefectural capital, medical and educational facilities are all present within easy reach.

Wall length is exhibition capacity. Having 285 metres on which to hang work means being able to programme at that scale, and it constrains what a curator can propose far more directly than floor area does — a large room with short walls is of limited use to a gallery. Museums are usually compared by floor area, because that is the number that gets published and the one that sounds impressive. If you want to know what an institution can actually put in front of people, the quicker and more honest measurement is the length of its wall.