#12359 | posted by  Yubi | 8 years, 8 months ago on Are there any onsens (natural hot springs) located close to…

There is one Hotel Dormy, halfway between Akihabara and Okachimachi stations, with an onset on the rooftop. But this one is not natural. As @BanzaiTokyo mentions, this will not be as calm and relaxing as one in the mountains. For that, you can visit Mount Takao or Mount Hinode, about an hour from Tokyo.