This steep-sided canyon was carved by the Colorado River in Arizona over millennia.
It is over 400 kilometres long and almost 2,000 kilometres deep. The canyon and its caves are full of Native American settlements. It is the only one of these seven natural wonders that have been inhabited for centuries. Where to see: Arizona, USA
From Hawaii to Australia, India to Namibia, these destinations around the world are downright terrifying and sometimes even deadly, home to rampant shark attacks, eel-infested waters, deadly currents and toxic waste.