Swiftcurrent Lake in Glacier National Park, Montana, USA

The dense forests, towering Rocky Mountains, and alpine lakes of Glacier National Park show the stark ecological distinction of western Montana when compared to the open vistas of the eastern half of the state. Swiftcurrent Lake, seen here under unusually dark cloud cover, is one of 130 lakes dotting the expanse of the park’s 1 million acres. A day hike here is just scratching the surface of all that Glacier National Park has to offer. But if you’re nearby and want to get a taste of the “crown of the continent,” all US national parks are offering free admission this week. So, really, there’s no better time to get out and discover your national park.