Good ideas for a weekend trip

Hello,

I am now together wih my girlfriend here in Japan for several weeks.

We are living in Tokyo and want to do a weekend trip in October somewhere where we can relax a little bit.
Since she has to work on most weekends, we want this trip to be something very special, which we can still remember for a long time.

We are planning to leave either Friday evening oder Saturday morning, so we haven't decided if we want to sepend two days in a hotel or just one.

We would prefer something like a nice traditional Ryokan and a really nice Onsen. We would also be willing to pay more, if we could have something like a private Onsen.

So do you have any good recommendations what would be a good place to go?

A trip I'm planning on taking myself is to Hoshi Onsen in Gunma-ken. Their indoor mixed gender bath looks beautiful.

http://www.houshi-onsen.jp/