Bunkyo Civic Center is a ward office with an unexpectedly good free view from its 25th-floor observation deck. The building itself is a bulky bit of late-20th-century civic architecture, but the reason to come is the panorama: central Tokyo spreads out below, with Shinjuku's towers to one side and, on clear winter days, Mount Fuji beyond them.
It is a practical alternative to the city's paid viewpoints. You will not get the height of Tokyo Skytree or Tokyo Tower, but you can walk in, ride up, look around, and leave without turning the view into a half-day production.