Shinjuku is home of the tallest office buildings in Tokyo, most of which are located in the famous Western side of the Shinjuku district. The Tokyo Metropolitan Government is located in the twin towers and the top floor houses the observation decks open to public access, yes for FREE.
First the details
Address : Tokyo Metropolitan Government Building No.1, 2-8-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo
Admission : 0 yen! Free of Charge
Open : South Observation Deck: 9:30 a.m. – 5:00 p.m. North Observation Deck: 9:30 a.m. – 10:30 p.m.
Closed : South Observation Deck : 1st and 3rd Tuesday North Observation Deck : 2nd and 4th Monday
If these days are national holidays then the next day.
Access : The observatory is accessible on foot from Shinjuku Station (12-15 minute walk) and we prefer the Tochomae Station on the Toei Oedo Line from where it is a 2 minute walk to the observatory.