Tokyo Government South Observatory 東京都庁 南展望室
Similar to the North Observatory, the South is free as well, but gives a different view as it is located in an adjoining tower. The South Observatory is closed on the 1st and 3rd Tuesday of every month and hours of operation are shorter than the North: 9:30 - 17:00. However, on days that the North observatory is closed, they extend the hours until 23:00.
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A great view for the price of-- oh! It's free! There are cute souvenirs at the top, though are relatively pricey in comparison to other locations.