Besides 1 night free when you stay 4 nights, Platinum Bonvoy Members get room upgrade (love the Kamogawa River view), free breakfast (it got a bit boring after 4 days and we skipped breakfast on the last day).
We joined the Sunday activities: soap making and a short art tour. Love the special chandelier. The lighting in the hotel is superb.
Had my dose of Pierre Hermé macarons there too.