As natural phenomena go, Saltstraumen plays in the premier league. Like the whirlpool of Nordic giants, this soul-stirring wonder is the world’s strongest tidal current, with 400 million cu metres of water rushing through a sound that links two fjords at speeds of up to 20 knots (37km/h). For a thrill, notch up the speed bouncing past it at close range in a RIB (rigid inflatable boat), with the silver-grey ripple of mountains a beautiful blur on the horizon.