And hereunder has some more information.
Onsen Hotspring including mixed bath
This page to introduce easy but real natural onsen experience in Tokyo.
No JR Pass, no problem, as they are located within Tokyo. If you had one
day extra in your itinerary, it is truly worth dipping yourself in one
or even more of below. The last on this lists is, of course, Asakusa.Though
the best Jakotsuyu did shut its management of 100 years, there are still
couple of them in Taito-ku where Ueno and Asakusa are located, one of 23
districts of downtown Tokyo, is truly a mecca of onsen/sento.
For those who would like to jump and soak with swimming suit (swimming pants), please find no-shy-at-all both Hakone Kowakien Yunessun and Niwa-no-yu (neither of them is Japanese authentic traditional style).
With tattoo? Bit problem here in Japan, but you may find tatoo-friendly.jp useful. Nearby Narita Airport has Yamato-no-yu. In Asakusa, popular KotobukiYu is the best but not technically onsen hot spring, it is actually good mineral well water, with which local tofu is produced.
HaginoYu (nearby Uguisudani, between Ueno and Nippori on JR Yamanote Line)
One of the biggest and the newest/cleanest sento in downtown, opened in 2017. Morning has good deal for sauna, no extra cost, which means that you may enjoy sauna within basic price of JPY470. Lunch and Dinner cannot be missed because they are all handmade, real cooked in their kitchen, not microwaved prepared food. Operated by same family of KotobukiYu (between Ueno and Asakusa) also highly recommended.
YakushiYu (in Mukojima, nearby SkyTree Tower)
Just crossing over Sumida River from Asakusa, located north of the tower. Not onsen hot spring but using undergroundwater -80m below, surely good for your skin rather than just tap water, and surprisingly still boiling with firewood.
Somei Onsen Sakura (nearby Komagome or Sugamo on JR Yamanote Line)
Just 4-5 minutes short walk from the Yamanote Line station/s, even they have free shuttle bus from/to Sugamo station, right in the middle of residential square, this would be your cozy treat with green garden attached and tatami room relaxation. Tattoo strict (very strict). Tabaco free. Delicious matcha softcream available (^^)
Miharadai Fuji-no-yu (in Shakujii)
The old bathhouse with Japan nostalgia, not natural hot spring, though. Please also find Asakusa Onsen in text below with real mineral water springing from 1,000 meter down.
Ryusenji-no-yu (in Souka or Soka)
Easy and cheap access from Asakusa on Tobu Skytree Line (bound for Nikko). Yatsuka (TS15) is only 30 minutes, only JPY320, one way from Asakusa. Or, Soka (TS16) has free shuttle bus from/to the onsen hot spring.
Kinu no yu (only bit out of downtown)
Also easy access from Asakusa on TX (Tsukuba Express) train. It is 28 minutes train ride to the nearby station Moriya, and there is a free shuttle bus taking you from/to the hot spring. Only the onsen in Ibaraki-ken which uses no-recycling natural mineral water. Not in downtown, but much much better than Oedo Monogatari Onsen in Odaiba. Mix onsen is available.
Maenohara Onsen (Sayano-yudokoro)
Another easy access? Located just outside of downtown, well, still within Toei Subway network, we also would like to recommend this off-beaten-track hot spring. It is 45 minutes subway rides (Kuramae => Kasuga => Shimurasakaue) Toei Oedo Line and Toei Mita Line. Much much traditional compare to Oedo Monogatari Onsen in Odaiba.
Yumorinosato (in Musashino)
Located in a bit west end of downtown, it is rather easy to access if you are in Shinjuku and Shibuya area already. Keio Line has easy access from both terminal stations, and Chofu station has not only this hot spring but also Chofu Airport for Tokyo's southern islands as well as Ajinomoto Stadium (FC Tokyo's home ground).
Kamata Onsen (in Ota-ku)
Situated in southern most district of downtown Tokyo, this onsen has been managed by one family since 1937. In Japanese, we call this onsen ....... KuroYu (BlackOnsen) as color is just like coffee. Not far from Moriyama House.
Sento (Sentoh or Sentou) and Onsen in Meguro-ku
Feel bit itcy after visiting Parasitological Museum in Meguro? Let's wash them out here and there in Meguro-ku. Please note some of the lists has not mineral water but tap water (>_<)
Okutama Onsen MoegiNoYu
JR train reaches to this western edge of Tokyo. From skyscraper Shinjuku, it is just less than 2 hours train ride, you'll be middle of forest and along Tama river stream. Tired of walking on asphalt in concrete jungle? Your zen relaxation is just JR away!
Takao Onsen GokurakuYu
Another western edge of Tokyo is this popular mountain hike spa. Keio Line goes direct from Shinjuku. You may try hiking over TakaoSan (Mt.Takao) for your green life in Tokyo.
There WAS a hot spring nearby Tokyo Ryokan. It WAS the real onsen using hot spring, mineral water, from 1,000 meter underneath of Tokyo city. But this famous and popular Jakotsuyu was closed in May 2019. Although, please don't you worry, there are several others still available here in downtown (including tattoo friendly one). It is only 470yen per one adult (sauna costs usually extra 200yen or so). Some has within short walk distance from Tokyo Ryokan . It is Japanese culture to crash down after sento (sentoh or sentou) or onsen. Among them, KotobukiYu is the top listed, nearest metro station is Inaricho (G17), nearest JR station is Ueno. HinodeYu as well. Here's the Google Map.