Best onsen regions in Japan

Last year we went on a wonderful, onsen-focussed trip to Kyushu and absolutely loved it. We went to all kinds of sentos and onsen around the island - from small neighbourhood ones to mega onsen as part of big hotel chains (the likes of Suginoi group) to truly amazing ryokan (Yamamizuki).

We have started planning a similar trip for Spring of next year (likely May). I am looking for a region that has lots of onsens that I can visit (either as day visitor or as an overnight guest).

My questions:

1. Apart from Kyushu, what are other regions of Japan that have a great concentration of Onsen? I know that Onsen are spread throughout the country, I am looking for world-class and unique ones.

2. What are some of truly world-class onsen/ryokan you would recommend? I am looking for an experience similar to Yamamizuki Onsen in Kurokawa.

Have you bothered to do a simple google search for famous Japan onsen?

There are many websites that offer "top 10" lists for places to go. However, most of those lists (in my experience) are tailored a little for foreign visitors, and do not include some of the places popular or well known by Japanese people. There are enough locations across the country for you to go pretty much anywhere.

Start here: https://www.japan-guide.com/e/e2292.html

As it happens, I *have* done basic searches such as "Top Onsens in Japan" and "Top Onsen regions of Japan". The reason I asked the question here is that I was not happy with the answers.

"Top Onsen in Japan": This tends to return a bunch of SEO optimized sites that list onsen all over the country. These pages seem to mainly be interested in selling me ryokan/onsen reservations, and less on listing unique onsen.

"Top Onsen regions of Japan": Not so good results. I have heard speaking to Japanese people that Kyushu and Tohuku are good regions. But none of my searches turn up these regions.

I would look into the following regions:
- Around Tazawako in Tohoku. Depending on how far you want to travel you can pop in as well Ginzan onsen and a stay in Hiraizumi and/or Tono valley (Tono valley not for onsen, but for wonderful landscape). Hiraizumi, there are onsen, but more importantly a number of famous but not overcrowded temples and shrines.
- Hirayu onsen. There are many different onsen there, mostly focused on rotenburo in the mountains. Additionally you can go hiking in that region (or skiing). Again depending on how far you want to travel/how many days you are staying, you could go to Kurobe Gorge take the train inside and stay at one of the ryokans inside. I stayed last year at one half way out of the gorge where you could see monkeys playing around below in the river, while soaking in a hot onsen.
https://bicycletraveljapan.blogspot.com/2017/10/day-27-kurobe-gorge.ht...
- Not so much an onsen region, but I would say this one was the best onsen I went to outside of Kyushu (the best in total was Yamamizuki and others in Kurokawa onsen), is the one in a buddhist monastery on osorezan. The water is very acid (I think something like pH 2). They say to only soak for a few minutes... well, I didn't take the advise and enjoyed several really great baths. No rotenburo, but the huts where the onsen are in, are just outside of the temple in middle of this moonlike landscape on a bubbling volcano. It doesn't get better for me. However the region is hard to reach, and I am not sure if there are other onsen that merit a visit around.
https://bicycletraveljapan.blogspot.com/2017/10/day-13-hakodate-to-oma...
https://bicycletraveljapan.blogspot.com/2017/10/day-14-osorezan-to-noh...

Here a list of all onsen I went to while in Japan:
https://bicycletraveljapan.blogspot.com/2017/09/onsen-ranking.html
My travel wasn't primarily geared towards onsen, and what I most like about onsen is the rotenburo. An onsen without it (or with a very small one) isn't attractive to me, regardless of water quality.

I am sure there are many other interesting onsen spots, but these are the ones I have experience in.

Enjoy your soak!

Thanks, @LikeBike. Those are some amazing suggestions.

The Kurobe Gorge especially sounds lovely. My other interest apart from onsen is trains.

Re: difficult to get to, we don't mind going a little out of the way to find truly great onsen.

We'll probably be flying into Aomori, renting a car and driving down stopping at onsen on the way south.

My favorites are:

- Towada-Hachimantai National Park: onsen highlights include Tamagawa, Nyuto, Goshogake, Fukenoyu and Sukayu.

- Gunma Prefecture: especially Kusatsu and Manza Onsen, but also Minakami, Ikaho and other

we have been to quite a few (my favorite was also in Kurokawa, but it was Hozentai which I think Winter Visitor recommended).

I dont know whether you like onsen hopping (not really my cuppa) or just a great ryokan in an onsen town (unfortunately some dont have onsen water in them, eg the ryokans at Kinosaki Onsen). My preference is a nice ryokan with onsen water in a nice town, or maybe a nice hotel with onsen water.

so against that, the ones that come to mind are the Onsen Hotel at Kamikouchi (great rotenburo with monkeys in the trees sometimes), Hotel Associa at Takayama (onsen baths on balconies overlooking the town - really pretty when the snow is falling), and Hotel Hakuchoro at Kanazawa (very dark tea coloured water). There are plenty of other smaller ones (eg one at Karatsu where you soak while looking out over the bay, some of the onsens at Bessho Onsen have nice views over the town, Lalaca at Gora had nice outlooks for the baths), but they were the big ones I really liked.

Thanks @Uji and @Lazy Pious. Those are the kinds of recommendations I was looking for. Even if we may not be able to go all of them in our next trip, we will add them to one of our future trips for sure.

Here are my suggestions based on regions:

Hokkaido: Noboribetsu - this is close to my favourite location for waters in Japan

Tohoku: Nyuto Onsen & Tamagawa Onsen has nice waters. Note that Tamagawa Onsen has close to the most acidic waters in the country. I've also heard good things about Zao Onsen

Kanto: Manza & Kusatsu Onsen are great. I am also aware that it's expensive - but I also like Hakone. Strangely the best water I found was at a hostel.

Chubu: Nozawa Onsen has reasonable waters. So does Kaga Onsen. My knowledge of good onsens in the province is limited

Kanto: There is a hotel in Kii-Katsuura which has nice waters in a huge cave that overlooks the pacific ocean. If the waves are large then the water from the ocean comes into the caves. This was a special place. Kinosaki onsen has very average waters but is a pretty town with lots of public baths

Chugoku: Kaike onsen was ok in Tottori. I've not visit enough quality onsen towns here to comment strongly

Kyushu: The stands outs were Unzen and Takeo onsen. I've not visited Kagoshima or Kumamoto yet.