Board a traditional houseboat for a Kuttanad backwater cruise; most private boats allow boarding by 12:00–2:00pm — confirm exact boarding time with operator.
Take a guided boat safari through Kumarakom Bird Sanctuary (visitor center open approx 6:00am–5:30pm); excellent for herons, storks and migratory ducks — morning boats are best.
If you want a cultural stop, visit Ambalappuzha Temple for evening darshan (temple hours generally early morning and again in the evening — confirm locally for exact darshan times).