Just to the N.E. of Lake Myvatn, is NAMASKARD.  This is an area of sulphur wells, hot springs, fumaroles & bubbling mudpots.
Though intensely fascinating, this might be described as "Hell on Earth". Here you must keep to the paths, as the earth's crust is scarcely thicker than eggshell & your foot could go through into dangerously hot water.Unpleasant smells abound & visibility is often restricted. Not a place for a teacher to take a bunch of unruly kids; though on second thoughts, it might be JUST the place!!