One of the "must-do" activities in Kerala is a backwaters tour. While I don't know about "must-do", it was definitely nice and interesting to see life along the many water channels. The boat we booked, however, was a rip-off and the tour disappointingly short.
oh, a backwaters cruise is certainly a "must-do" - sad that yo got ripped off - best is to take an overnight cruise - that way you get to see the sunset on the backwaters and spend the night in the gently-rocking boat which is anchored close to shore...
and these photographs are lovely! esp the ones with the ducks...