Leave Chennai in the evening to avoid daytime city traffic; you’ll head toward Coimbatore via NH48 (overnight drive). This gives you a fresh morning near the hills before driving up to Munnar.
Reach the Coimbatore area early morning and check into a budget/day-use hotel for a few hours' rest before driving into the hills (hotel check-in early by arrangement).
Guided boat cruise on Periyar Lake to spot wildlife along the shoreline; boat timings run typically in the morning and afternoon (park open ~7:00am–5:00pm).
Private day cruise through the famous Kerala backwaters (not overnight) — a peaceful boat trip past paddy fields, coconut groves and village life; boat trips operate through the day (09:00–17:00).
Estimated total costs below are based on these assumptions: family of 4 (2 adults + 2 children), you drive your own sedan with average fuel efficiency 15 km/l, petrol price assumed INR110 per litre, route distances approximated from Chennai → Coimbatore → Munnar → Thekkady → Alleppey → Chennai with local travel included. All activity/hotel prices are mid-range estimates — book in advance for best rates.
Book hotels in Munnar and Thekkady in advance (Oct is a popular window), reserve Periyar boat and Alleppey backwater privately to ensure family seating, and plan driver rest shifts. If you prefer less overnight driving, consider cutting one hill stop and staying nearer to Coimbatore and driving back daytime.