By far the most alluring attraction of Stockholm’s Solna Centrum shopping mall is the Blue Line Metro station that has served it since 1975. Artists Anders Åberg and Karl-Olov Björk painted the exposed bedrock of the underground concourse a thrilling and beautifully lit night-time red. Riding the escalators here is like being drawn into, or escaping from, some mythical sorcerer’s cave. Since 1957 more artists than it would take to fill the carriage of a Metro train have conjured 94 of the network’s 100 stations into memorable public artworks, justifying the widely quoted description of the 70-mile Stockholm Metro as «the world’s longest art gallery». Perhaps only the Moscow Metro, mostly of an earlier era, rates alongside this remarkable achievement.