Arima Onsen Ginsuiso Choraku
有馬温泉 銀水荘 兆楽
The clearest answer in Arima, and it comes from the ryokan itself: the large baths and the communal open-air bath are closed to tattooed guests, and its own FAQ then names the alternative — take the reservable open-air bath instead, which costs extra. Nothing to cover, and nothing to explain at the door.
入れ墨・タトゥーがある場合は? 大浴場・露天風呂のご利用は頂けません。有料となりますが、貸切露天風呂をご利用ください
Best for: Any size of work, without a conversation — the ryokan has already had it
There are rooms with their own open-air bath too, in a detached annex, if you would rather not book a slot at all. The reservable bath is its own building among the trees.