Fish River Canyon is the largest canyon in the Southern Hemisphere, second only in the world to the Grand Canyon. The whole gorge measures 160km (99 miles) in length and is 127km (79 miles) wide, whilst its impressive inner canyon is an amazing 550m (1804ft) deep. The gorge which has formed over hundreds of millions of years, winds through the arrid desert landscape, cutting through the great plateau and surrounded by imposing cliffs and large boulders. The site is the main tourist attraction in the far south of Namibia, popular with hikers who set out on the testing trail through the canyon. At the southern end of the canyon, after a long hike through the desert terrain, weary walkers arrive at Ai-Ais (meaning Burning Water in the local Nama language), a hot water spring which wells from the earth and is believed to cure rheumatism.