Where is downtown Tokyo?
The picture is Shinjyuku 新宿 from Akasaka 赤坂 Area.
Tokyo has many downtowns but all located inside the Yomanote loop (山手線).
Yamanote Line ... Staring from Tokyo Station going clockwise.
Tokyo
Yurakucho
Shimbashi
Hamamatsucho
Tamachi
Shinagawa
Osaki
Gotanda
Meguro
Ebisu
Shibuya
Harajyuku
Yoyogi
Shinjyuku
Shin-Okubo
Takadanobaba
Mejiro
Ikebukuro
Otsuka
Sugar
Komagome
Tabata
Nishi-Nippori
Nippori
Uguisudani
Ueno
Okachimachi
Akihabara
Kanda
Depending in the interest, you must choose which downtown or station to get off. Here ares one of the websites in English.
http://www.japanvisitor.com/japan-travel/yamanote-line
https://blog.gaijinpot.com/exploring-tokyo-yamanote-line
Or you can do your own search using "Yamanote Line " as a key words.
Japanese-Online Blog: http://en.bloguru.com/japaneseonline/