Isolated, polluted and – above all – cold, it is a city built on misery and blood. It is also a city of surprising wealth – the reason for its unlikely existence. Norilsk, squatting 250 miles north of the Arctic Circle, has the largest deposits of nickel, copper and palladium on earth and its hellish mines are thriving. Gulag prisoners began expanding the Siberian settlement in 1935 and over the next 20 years, 500,000 slaves took part in its construction . Thousands lost their lives.