In this large city with such an efficient public transportation system, walking to get from point A to point B would seem a bit stupid at first glance.
However, as the city is extremely safe even at night, walking in Tokyo can be a very pleasant experience.
In some areas, walking can be much shorter than taking the subway and walking the transit (the whole Akasaka/Nagatacho/Roppongi area in the center is for instance very easily covered on foot).
If you have the time, Shinjuku to Shibuya via Omotesando takes roughly one hour, Tokyo Station to Shinjuku would be a half a day walk, and the whole Yamanote line Grand Tour takes a long day.
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