Volcanoes. At their gentlest, they're grumbling, ash-puffing menaces. At their worst, they can rain fiery destruction and bury cities. And yet when I heard you could descend right into the belly of a volcano in Iceland, I couldn't slap on a helmet quickly enough. I admit it. This was no daredevil feat. Thrihnukagigur volcanois dormant and has been for thousands of years. The highest risk factor is probably the humiliation of trying to pronounce 'Thrihnukagigur' (which sounds