I think that would be a great experience Athena...
You're right...some ryokans don't offer private facilities...but many do...
I often pay a bit extra and stay at a ryokan that offers private facilities.
I often stay at a ryokan in Kyoto that has a communal bathroom...but, it's not really a problem - there are only 4 rooms so, a maximum of 8 guests...you have a designated time in the evening to use the bathroom, which is always spotless...
The strangest thing was finding the bathroom closed in the morning!
Also, there are usually toilets near your room and often, a basin in your room - it's often just the shower & bath in the communal bathroom.
I doubt I'd share a bathroom in any other country....but in Japan it's all so organized and clean...
I don't like using the communal bath water so, unless I can reserve a private bath...I settle for an awkward session with the hand held shower...it's always too low to just stand under...
The Japanese Inn Group have a great website - you can view the ryokans in your area and book on line...
The minshuku rarely have private bathrooms and are aimed at the budget traveller.
I'm working in Japan from the 29th of this month - my mother is joining me - I've chosen lots of traditional accommodation so she gets a real Japanese experience including, a stay at an Onsen (hot springs bathing)in the Japan Alps...I don't like communal hot springs bathing so, have opted for an Onsen that offers private bathing...
It really is a fascinating country and after sooo many visits, I still look forward to my next trip.
See you in Japan!
