Board the Serenity boutique day cruise for Lan Ha Bay: scenic limestone karsts, caves, swimming, kayaking and included lunch on board; cruise schedules generally run morning–late afternoon (approx 8:30am–5:30pm).
Explore the Japanese Covered Bridge, assembly halls and historic houses; many heritage sites use a ticket set (visit hours ~8am–9pm depending on sites).
Drive briefly to Da Nang for the lit-up Dragon Bridge (fire-breathing show usually Sat & Sun nights at 9pm — check schedule). Otherwise enjoy lit skyline views.
Morning direct flights are available (or via HCMC) — aim to arrive in Hanoi around midday to meet your requested finish time; confirm flight times when booking.
If you have time, a quick bowl of pho or final Hanoi snack near the airport or city is a great send-off; otherwise transfer to your next destination/airport.
Tour ends midday in Hanoi per your request. If you need airport transfer, extra nights, or luggage storage, arrange with your hotel or a local operator.