Red Rocks Amphitheatre

Two 300-foot sandstone fins frame the stage at Red Rocks, an outdoor amphitheater carved by geology rather than any architect. U2 filmed "Under a Blood Red Sky" here, and the recording captures why: the acoustics are a geological accident that nobody has managed to replicate. The venue sits open most of the year for hiking and visiting even when nobody's performing, so you don't need a ticket to feel like you've stumbled onto something.