Sylvan Lake, known as the "crown jewel" of Custer State Park, is located in the Black Hills of South Dakota. Created in 1881 when Theodore Reder built a dam across Sunday Gulch, it offers picnic areas, rock climbing, small rental boats, swimming, and hiking trails. It is also popular as a starting point for excursions to Black Elk Peak and The Needles.

The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming. Black Elk Peak, which rises to 7,244 feet, is the range's highest summit. The Black Hills encompass the Black Hills National Forest. The name "Black Hills" is a translation of the Lakota Pahá Sápa. The hills were so-called because of their dark appearance from a distance, as they were covered in trees.