Holy Resurrection Cathedral, often called Nikolai-do, is Tokyo's main Russian Orthodox cathedral. The restored 19th-century building stands near Ochanomizu Station, with a green dome and Byzantine form that feel very different from the shrines, temples, and office blocks around it.
It is an easy architectural stop between Akihabara, Kanda, and Jimbocho. The nearby Hijiribashi bridge is also worth a look, especially in the evening when the rail lines and city lights frame the area.