Any mixed-gender (konyoku) onsen near Tokyo?
Have been living in Tokyo for many years but have not found any authentic mixed-gender allowed 'natural onsen' near Tokyo (not looking for private hot tubs). Me and my wife love to travel and probably have been to more than 100 onsens in Japan. Due to work schedule, we can only manage day-trips and we want to spend as much time as possible together. But in gender separated onsens, we have to spend 1 hour to 1.5 hours without talking with anyone, which feels kind of boring no matter how good the onsen is.
Found some information online, but want to know first-hand experience from people who actually have been mixed-gender (couple) onsen. Our ideal place will be natural hot-springs near river, or open 'rotenburo' (not closed by walls) from where we can have a great view of the nature around.
Any recommendation with actual experience will be appreciated.