For Manhattan-based travellers, New Jersey offers some of the best day trips out of the city. Princeton is an hour by NJ Transit, with a beautiful walkable campus and a pedestrian-friendly downtown. Liberty State Park in Jersey City is the easiest base for a Statue of Liberty / Ellis Island visit, and offers the best free skyline views in the region.
The Delaware Water Gap in the northwest is two hours from New York City — a half-day of hiking, river kayaking or a scenic drive. Cape May at the southern tip is a long but rewarding day from the city or Philadelphia, particularly in spring or autumn for the migrating birds.
Travelling the other direction, Philadelphia is just across the Delaware from Camden — easy by train or bus from Trenton or Newark.