Morning flight from Delhi gives you a full first day in Kerala; flights vary, book early for December. Aim for an early arrival to maximize sightseeing time.
A relaxing boat ride on Periyar Lake offers good chances to spot elephants, deer and birds along the forest edge — boat rides run from early morning through late afternoon (confirm slots on arrival).
Watch a traditional Keralite martial-arts (Kalaripayattu) performance or local cultural show in Kumily (if available) — check show times locally (usually evening).
Board a private traditional Kettuvallam houseboat for an overnight romantic cruise; lunch is served onboard and usually included in the houseboat rate.
Drift through narrow canals and paddy-lined waterways, watch village life and enjoy serene privacy; houseboat cruises usually run midday to next-morning (confirm check-in times; typical check-in ~12:00–13:00 and checkout ~09:00).
Some houseboats stop at small villages for a short walk, or you can request a short canoe/kayak trip (subject to availability) — a great couple's experience.