Great Bear Recreation Park gives Sioux Falls a small but real outdoor playground on the city's northeast edge. In winter it operates as a ski, snowboard, and tubing hill; outside the snow season, the same folds of land are used for walking, mountain biking, and views over the Big Sioux River valley.
Do not expect mountain-resort scale. Its value is local and practical: a place where you can add a few active hours to a city stay without driving far, especially if you are travelling with children or need a break from downtown sightseeing.