Dormant Arenal Volcano sunrise over Lake Arenal and rainforest, Costa Rica

Ssh, it's sleeping

The day is young, and so is the mist-shrouded mountain in the midst of this Costa Rican rainforest: Geologists can only trace Arenal Volcano's eruptive activity back a little over 7,000 years. Given that some elder volcanoes are more than 2 million years old, Arenal is just a toddler (though at over a mile high, it was a fast grower). This tall tyke has been prone to tantrums in the past, erupting almost continuously for more than 40 years starting in 1968. But in 2010 the fumes finally shushed, and Arenal has napped peacefully since.