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
Whether you're drawn to the romance of cobbled streets, the architectural marvels of centuries-old buildings, or the vibrant tapestry of diverse cultures, Europe's cities stand as a testament to its rich heritage.