The Derweze area is rich in natural gas. While drilling in Soviet geologists tapped into a cavern filled with natural gas. The ground beneath the drilling rig collapsed, leaving a large hole. Locals have dubbed the cavern "The Door to Hell".
Kayaking along Pictured Rocks National Lakeshore, Upper Peninsula, Michigan. I did this for vacation last year. It's an eight hour day trip along the Pictured Rocks. Breath taking and well worth the money you spend on the experience!