One of the world's largest ice festivals has opened in north-eastern China for a month-long run. br Millions of visitors flock to Harbin every year to see the winter wonderland, which features frozen castles, glistening snow sculptures and even penguins. br There's also a winter swimming competition, with more than 300 people braving the chilly waters.br Harbin is one of China's coldest cities, with temperature dropping as low as minus 35 degrees Celsius.