Ponder the mystery of ancient civilizations at America’s Stonehenge, an outdoor history museum of stone structures and astronomical alignments built more than 4,000 years ago. But who built this maze of manmade chambers, walls and ceremonial meeting places that still is an accurate astronomical calendar? Was it an ancient American civilization or a migrant European population? No one knows, but it’s a great puzzle to try to solve as you take a self-guided audio tour. The half-mile trail is over uneven rocky terrain and takes about an hour. There’s an 11-minute introductory video on the website. There’s also snowshoeing on the site and: seven friendly alpacas! For a special outing, consider visiting during the summer or winter solstice.