Mt.Takao is definitely the most famous and most popular mountain for hiking not only in Tokyo metropolis but in Tokyo metropolitan area. It is located at western Tokyo, in the city of Hachioji, a part of Meiji no Mori Takao Quasi-National Park. The annual visitors = hikers is over 2.6 million which is the highest in Japan and most likely highest in the world too.
It was registered as Japan Heritage in 2020, the first heritage in Tokyo metropolis. Probably the reason of popularity is that Takao-san Yakuin-Oin temple is located on the middle of the mountain. Therefore hikers can enjoy hiking and worship at once. There are 7 routes to reach the summit, which takes 90 minutes to 120 minutes from the bottom.
Another reason of the popularity is that Mt.Takao has a good access from downtown Tokyo. For Japan Rail Pass holders, take a Chuo line train to Takao and change to Keio Takao line to Takaosanguchi station. For non-JR pass holder, take a train bound for Takaosanguchi from Keio Shinjuku station. There are funicular and chairlift stations 5 minutes away from Takaosanguchi station. Please be aware that both funicular and chairlift will not take you the summit but just to 470 meters above sea level.