The Zimmerli Art Museum on the College Avenue campus is the best free museum in central New Jersey. Its strengths are 19th-century French art (with a particularly good collection of late academic and early Impressionist works), American art, and the extraordinary Norton and Nancy Dodge Collection of Soviet nonconformist work — artists who painted against the Socialist Realist orthodoxy from the 1950s through the collapse of the Soviet Union.
Admission is free and the museum is generally open Tuesday through Sunday. It is comfortably sized — two to three hours sees most of what is on display — and a good rainy-day option in a town that is otherwise short on indoor sights. The cafe is small but adequate.