Want to hit the slopes during the summer? Try Great Sand Dunes National Park and Preserve. These 750-foot dunes—the tallest in the U.S.—are the perfect place for sandboarding and sand sledding. When the afternoon sand heats up, head down to Medano Creek, where mountain snowmelt creates a natural beach for swimming and building sandcastles. Plan to be in the park at night, too. The air is so clear that you can see the Milky Way light up the sky. “This place is tailor-made for kids,” park ranger Patrick Myers says. “There really is a unique sense of uninhibited freedom here.” —Brian McGrath