The day-by-day plan
1–2
Hanoi
Settle in after arrival. Use the full city day for Hoan Kiem, the Old Quarter and the Temple of Literature, with a cooling café break. Do not count arrival day as a full sightseeing day.
3–4
Ninh Binh
Travel to Ninh Binh, choose Trang An or Tam Coc and leave time for the countryside. Return to Hanoi on day 4, avoiding a long early transfer to the cruise the next morning.
5–6
Ha Long Bay
Take a two-day, one-night cruise with the pier and transfers confirmed. Return to Hanoi after disembarkation on day 6, without a tight international flight connection. Keep a Hanoi cultural alternative if sailing is cancelled.
7
Hanoi
Keep the last day for a final coffee, a short revisit and the airport journey. With an early flight, leave directly rather than forcing in one more sight.
Make it your own
To include Sa Pa, add at least three days or replace the bay segment. An overnight mountain journey is still travel time and requires recovery.