Mitama Matsuri (みたままつり) is a popular Obon festival in Tokyo. Obon is a commemorative festival to celebrate one’s ancestors in which Japanese believe the souls of the departed return home for a brief while. During the Mitaka Obon Festival you can find about 30,000 lanterns, lining the path from the food stall areas to the Yasukuni Shrine. There will also be Taiko drumming and a Mikoshi (portable Shrine). Besides the many food stalls you can also enjoy Haunted Houses and classic carnival games.
Mitama Matsuri is one of the most early Obon matsuri’s in Tokyo and usually takes place from July the 13th until the 16th. Make sure to check the date on their official website though! The Yasukuni Shrine is a 3 minute walk from Kudanshita Station (Shinjuku Subway Line, Hanzomon Subway Line and the Tozai Line).
Official Yasukuni Shrine website (in English): http://www.yasukuni.or.jp/english/index.html