River rapids ride is very popular in Japan. Then, there are two types of river rapids ride. The first one uses wooden boats and there is a staff who is controlling the boat and explaining the scenery during the ride. The second one uses rafts, canoes or kayaks. For middle age and seniors prefer more the first type and you can enjoy throughout Japan, mostly far away from sea.
Then, first type can be divided into two sub-types. Whitewater type or calm scenic type. If you are looking for whitewater type near Tokyo, Nagatoro's river rapids ride is the best choice. If you are in Kyoto or Osaka area, Hozugawa river is the best choice. Calm scenic type is best to try at Yanagawa, Fukuoka prefecture.
Make sure to purchase a ticket in advance at the box office. The boat do not depart until it reach the minimum passengers but mostly departs according the timetable. Also be aware where is the disembarkation point. The boat do not return to the departure point.