The extraordinary Unesco World Heritage city of Guanajuato was founded in 1559 due to the region's rich silver and gold deposits. Opulent colonial buildings, stunning tree-filled plazas and brightly colored houses are crammed together on to the steep slopes of a narrow ravine where excellent museums, handsome theaters and a fine marketplace punctuate cobblestone streets. The city's main roads twist around the hillsides and plunge into long dank subterranean tunnels, formerly rivers.