Just north of Marine on St. Croix is the popular and often busy William O’Brien State Park (16821 O’Brien Trail N., 651/433-0500). The original 180 acres were donated to the state by Alice O’Brien, daughter of the eponymous lumber baron, who purchased the land he had earlier cleared of trees.

The park, which has since recovered, has expanded to 1,579 acres. Though it only composes a small part of the park, the most interesting area is the beautiful and wildlife-packed floodplain forest.

The highly recommended Riverside Trail, a surfaced 1.5-mile loop with interpretive signs, offers up-close views of the river. Even better than walking along the water is getting right out on it. The easy paddle around Greenberg Island takes about an hour, though budget some extra time to poke around looking for wildlife and wildflowers.

There are canoe rentals, and a shuttle service lets you explore more of the river. Many people are satisfied just taking it easy fishing, picnicking, or swimming in Lake Alice.

The rest of the 12-mile hiking trail system forms a series of loops across the mosaic of forest, prairie, oak savanna, and wetlands stretching atop the bluffs. All of the trails have some rolling hills, but few are especially challenging. The most interesting and least traveled are along the west edge of the park.

The two-mile Woodland Edge Trail is mostly wooded, but as the name suggests, offers a look at the prairie as well, while the Rolling Hills Oak Savanna Trail, a mile-long loop through a savanna restoration, branches off the southern end of it. In winter most of these loops are groomed for cross-country skiing, both traditional and skating.

The pair of campgrounds, one down by the river and the other up on the hill, have 124 sites (61 electric) with a mix of shady and open choices in both; there is also a camper cabin. Overall, the last two loops of the Savanna Campground are the most peaceful and scenic options. The visitors center, open year-round, has nature displays and naturalist programs. For reservations, call 866/857-2757 or visit www.stayatmnparks.com.