Green and indoors
Hoan Kiem shore, Literature courtyards, Thong Nhat Park and Ethnology outdoor houses beat night lanes. Budget rest and air-con; go indoors at midday heat. Ethnology is west — a half-day alone, not jammed onto the end of an Old Quarter day.
What to skip
Skip late Beer Street, Train Street tracks, and long mausoleum queues (plaza exterior only if children cannot wait). Dress still covers shoulders/knees for the mausoleum. Night: a Hoan Kiem stroll or an early hotel return.