Hoshinoya

Best hotel in Karuizawa according to Alan Yung: but its price is quite steep (~HK$4.5k room only, not the best type of room facing the river but smaller rooms facing inside) and it has no hot spring in the room (has to walk to a public one also owned by the hotel outside the hotel area.

http://www.hoshinoya.com/en/info/index.html

Address : Hoshino, Karuizawa-machi, Nagano 389-0194, Japan
Tel : +81-267-45-6000 Fax: +81-267-45-6990