When the summer heat starts to cook every single body in Phoenix, an inborn signal goes off, much like the internal clock in geese that tells them to fly south to avoid the cold of winter. The easiest place to run away for the day is Flagstaff, but for a true break from the heat, your final destination shouldn't be the city proper. Head a little farther northwest into the Coconino National Forest to find Lava River Cave, a unique natural formation created when a volcano erupted some 700,000 years ago. As you head underground, be prepared for the overwhelming desire to bundle up underneath a cozy sweatshirt. The temperature in the caves is about 40 degrees Fahrenheit year-round, making them the perfect place to escape from the oppressive Sonoran Desert heat. This mile-long tubular cave is surrounded on all sides by hardened lava flows, so the surface is slick, bumpy, and totally unlike anything else you've ever set foot on. Wear comfy shoes, bring a jacket, and make sure to have a bright flashlight — better yet, one headlamp per person.