Frelinghuysen Arboretum gives Morristown a quieter counterweight to its Revolutionary War sites. The grounds spread around a Colonial Revival mansion on the former Whippany Farm estate, with lawns, specimen trees, flowering borders, woodland paths, and horticultural collections that are good for an unhurried hour or two.
It is especially useful if you want a low-key outdoor stop without driving far from town. The garden is large enough to feel like a real landscape rather than a pocket park, and the plantings change character through the year: spring bloom, summer shade, autumn colour, and winter structure all have their moment. Pair it with Morris Museum or Morristown National Historical Park if you are making a full day of the area.