O'Brien Observatory

The Marine Mill, established in 1839, was the first commercial sawmill in what became the U.S. state of Minnesota. Now in ruins, it is currently a historic site managed by the city of Marine on St. Croix in partnership with the Minnesota Historical Society. It was listed on the National Register of Historic Places as the Marine Mill Site in 1970 for having state-level significance in the themes of exploration/settlement, industry, and transportation. It was nominated for being the birthplace of the region's seminal industry—lumbering—and a major landing on its crucial transportation route, the St. Croix River. The site is also a contributing property to the Marine on St. Croix Historic District.

Croixsyde is a historic house in May Township, Minnesota, United States, near the city of Stillwater. It was built from 1922 to 1927 as one of the first summer homes on the St. Croix River. It was listed on the National Register of Historic Places as the Benjamin B. Sheffield House in 1980 for its local significance in the themes of architecture and entertainment/recreation. It was nominated for being an early example of the area's summer homes and for its fine rustic architecture.

Square Lake is a lake in Washington County, in the U.S. state of Minnesota.Square Lake was so named on account of its boxy outline.

William O'Brien State Park is a 1,520-acre (6.2 km2) state park of Minnesota, USA, along the St. Croix River. Its hiking trails traverse rolling glacial moraine, riparian zones, restored oak savanna, wooded areas and bogs. It is a popular place for birdwatching, picnics, camping, cross-country skiing, canoeing, fishing, and other typical outdoor recreational activities. The park is located approximately two miles north of the town of Marine on St. Croix, Minnesota.

The Apple River is a 77.5-mile-long (124.7 km) tributary of the St. Croix River in northwestern Wisconsin in the United States. Via the St. Croix, it is part of the watershed of the Mississippi River. It issues from Staples Lake in Barron County and flows generally southwestwardly through Polk and St. Croix counties. In northern Polk County, it gathers the Fox Creek near White Ash Lake and traverses several lakes throughout its course. The river flows through the city of Amery and the villages of Star Prairie and Somerset. It joins the St. Croix River 7 miles (11 km) northeast of Stillwater, Minnesota. In the Ojibwe language, the Apple River is called Waabiziipiniikaan-ziibi, meaning "River Abundant with Swan Potatoes". This name was translated into French, but only pomme (apple) of the French word for "potato" (pomme de terre—"apple from the earth") was translated into English. The Apple River was once an important route of trade for the logging industry; timber was floated downstream from logging camps in the north to a sawmill in Amery, Wisconsin where it was cut, loaded onto trains and transported throughout the region. Today, the river generates tourism revenue through recreation and resorts, attracting 500,000 visitors a year. Its relatively gentle rapids make it very popular for canoeing, tubing, camping, concerts, and is a popular fishing spot through all seasons.

Arcola Mills is a historic house in the unincorporated community of Arcola, Minnesota, United States. Built in 1847, it is considered the third-oldest and largest all-wood-frame house still standing in Minnesota. It was the home of brothers Martin and John Mower, who established one of the first sawmills on the St. Croix River and the community around it. The house and the remnants of the nearby mill were listed on the National Register of Historic Places in 1980 as the John and Martin Mower House and Arcola Mill Site for having local significance in the themes of architecture, exploration/settlement, and industry. The property was nominated as an "excellent example" of Greek Revival architecture and for its association with the region's early settlement and lumber industry. The property now operates as a non-profit event and education center.

The John Copas House is a historic house in the unincorporated community of Copas, Minnesota, United States. Its original owner was an Italian immigrant who settled the property in the early 1850s and built this house around 1880 to enlarge or replace his previous residence. The house was listed on the National Register of Historic Places in 1980 for its local significance in the themes of architecture and exploration/settlement. It was nominated for its association with John Copas, an early settler and leading figure in the community platted in 1857 and ultimately named in his honor.

Copas is a neighborhood of the city of Scandia in Washington County, Minnesota, United States. The Osceola and St Croix Valley Railway, which is part of the Minnesota Transportation Museum, goes through Copas. Minnesota State Highway 95 serves as a main route in the community. The John Copas House, built circa 1880 for the settler for whom the community was named, is listed on the National Register of Historic Places.

The Lee and Rose Warner Nature Center (WNC) was an outdoor education facility with a focus on natural history. It is located in Marine on St. Croix, Minnesota, northern Washington County about 30 miles (48 km) northeast of St. Paul, Minnesota. Warner was the first private nature center in the state of Minnesota. With funding from the Warner Foundation, at its closing WNC was the only nature center in the state of Minnesota to still provide free on-site programming to schools. On September 5, 2019, the Science Museum and Manitou Fund announced the Warner Nature Center would be closing, with operations winding down fully by December 31, 2019.

Arcola is an unincorporated community in May Township, Washington County, Minnesota, United States. Arcola is located in the southeast part of May Township along State Highway 95 (MN 95). The northeast part of Stillwater Township is also in the immediate area. Nearby places include Stillwater and Marine on St. Croix. Arcola was first settled circa 1847. The John and Martin Mower House and Arcola Mill Site, around which the community was founded, is listed on the National Register of Historic Places.

May Township is a township in Washington County, Minnesota, United States. The population was 2,670 at the 2020 census. May Township was organized in 1893, and named for Morgan May, an English settler.

The Soo Line High Bridge, also known as the Arcola High Bridge, is a steel deck arch bridge over the St. Croix River between Stillwater, Minnesota and Somerset, Wisconsin, United States. It was designed by structural engineer C.A.P. Turner and built by the American Bridge Company from 1910 to 1911. The bridge was listed on the National Register of Historic Places in 1977 for its national significance in the themes of engineering and transportation. It was nominated for its exceptional dimensions, beauty, innovative engineering techniques, and importance to transportation between Minnesota and Wisconsin.