Lately, I've been spending a lot of time hiking and bouldering in the Sourland Mountain Preserve in Somerset County. It's hard to believe you hit such a beautiful (and relatively mountainous) expanse of woods only 10 minutes outside of Princeton. What's really unique are the two significant areas of boulders (called the Devil's Half-Acre and Roaring River Boulders), which are for the most part, completely climbable with a little effort and ingenuity. New Jersey really is beautiful, and this is a fantastic site in which to enjoy it.
You can do the entire perimeter trail system passing both bouldering sites in about 10 miles, with plenty of connection trails back down to the interior and entrance if you get tired early. A fairly large area of the preserve extends beyond the bouldering sites, and you can walk through the brush easily with good shoes and long pants/high socks (I've seen a bit of poison ivy). Also, I noticed plenty of fruiting wineberries and garlic mustard and one black cherry tree (though it wasn't fruiting).
You can do the entire perimeter trail system passing both bouldering sites in about 10 miles, with plenty of connection trails back down to the interior and entrance if you get tired early. A fairly large area of the preserve extends beyond the bouldering sites, and you can walk through the brush easily with good shoes and long pants/high socks (I've seen a bit of poison ivy). Also, I noticed plenty of fruiting wineberries and garlic mustard and one black cherry tree (though it wasn't fruiting).