I'm travelling to Japan in 2 days with my boyfriend, and we will be there for a week. We're going to Tokyo/Kyoto/Osaka. It's our anniversary as well. We're looking for a nice onsen in one of these 3 cities. Would you recommend any special place? Thank you.
If you are going to Osaka. DEFINITELY VISIT SPA WORLD!!
But here's a handy recommendation guide for each city:
Top 10 Best hot springs in Osaka and near Kyoto .
Top 10 Best Hotsprings (Onsen) Around Tokyo
I Hope this helps!
If you are interested in a quiet Onsen place,
I recommend staying at Shima Onsen, Gunma prefecture.
There is a non stop bus that runs from Tokyo to Shima,
so it's easy to access. (It takes three hours and a half though...)
Kashiwaya Ryokan (Japanese style inn) is good.
It has three private baths (and these are free of charge!)
Staff are friendly, tatoo friendly (even in a public bath), cuisine is great.
Highly recommended :)