If you have never been to Helsinki, put it on your bucket list. But, go twice. Once in summer for 20 hours of sunshine daily and again in winter, when night rules and the Northern Lights dance across the sky in a riotous kaleidoscope. We recently made our second pilgrimage and arrived to find the locals cockahoop: the mercury had soared to 17 degrees, the ‘first summer heat wave’ of 2017.