Mount Vernon (day-trip) is a real time commitment — fit it in only if it's a priority.
Allow Half day (4–6 hrs incl. travel).
A beautifully preserved estate with the mansion, gardens and a genuinely thoughtful museum that doesn't shy from the enslaved-people's quarters — a satisfying half-day out of the city. The honest catch: it's a real trek without a car (bus-plus-shuttle or a tour), and the riverside grounds get hot and exposed in summer.