If you do nothing else in Iceland, do this! Our group was lead by Luis, who was excellent, striking just the right balance between professionalism (his team took real care to ensure we were properly kitted out) and humour, as well as explaining the geological significance of what we were about to see. After the 'in-water' safety briefing we were off and - spoiler alert - nothing could have prepared me for the clarity and general amazement of what we were about to see. Equally, Luis was always close by, ensuring we all knew where we were going and that we didn't miss anything. We had some other amazing experiences in Iceland (e.g. snowmobiling, lava exhibition, two spas, plus a geyser and plenty of waterfalls), but this was the highlight.