By train. From New York Penn Station, take an NJ Transit train on the Northeast Corridor line to Princeton Junction (about 50 minutes), then change to the Dinky — a tiny two-car shuttle that runs the three-minute hop from Princeton Junction into the campus station behind the Nassau Inn. From Philadelphia 30th Street, the SEPTA-then-NJ Transit route via Trenton is the usual approach (90 minutes).
By Amtrak. Some Amtrak trains stop at Princeton Junction, which is faster than NJ Transit but costs significantly more. For most people NJ Transit is the sensible choice.
By car. Princeton is about an hour from New York by Lincoln Tunnel and the New Jersey Turnpike, and an hour from Philadelphia by I-95. Parking inside the centre is limited and not free; the surface lots around the train station are the best option for day-trippers.
By air. Newark Liberty (EWR) is the closest major airport, about 50 minutes by car or about 90 minutes by airport bus and train. Trenton-Mercer (TTN) is closer but has very limited service.