I recommend the Beaver River Preserve in Richmond, Rhode Island. It’s owned by The Nature Conservancy. It’s rather small (240 acres) and the trail is rather short (2 or 3 miles). There’s no parking lot, but there’s roadside parking. It has a spectacular collection of boulders, most of which are probably glacial erratics; one might say that most of the Preserve is a boulder field. Many of the boulders have been split in two, probably by water freezing and thawing. The terrain is hilly, typical of a glacial moraine. In the western section of the preserve, in the middle of the loop trail, is a hill that may be a glacier-formed drumlin (in the map below, I marked this possible drumlin with a “D”).
When I was there, beavers had dammed the river, creating a large pond; the pond had lots of dead trees, interesting ducks (ring-necked ducks?), beaver lodges, and beavers swimming along with just their noses visible. There were many signs of recent beaver chewing — trees felled, bark eaten, etc.
A few traces of an old mill are visible. A mill race comes out of the pond, and is roughly parallel with the river for perhaps 100 yards, before joining the river; the beavers have dammed the mill race as well as the river. A few years ago, there was a rickety bridge over the river, and a short trail on the opposite shore, but the bridge is gone. This “eastern trail” may be accessible from Hillsdale Road, but its use is discouraged, and it doesn’t appear on the NatureConservancy map. (For more on this “eastern trail,” see Walks and Rambles in Rhode Island, p. 71, by Ken Weber, 3rd edition, 1999.)