This experience was absolutely incredible. The guides took care to ensure that the dry suits were a good fit. When I couldn't get a good seal on my mask, the guide traded with me so that I would be able to fully enjoy my experience. Highly recommend taking a waterproof camera. The water is ridiculously clear and it was great to bring back photos of this experience. There is a mild current, so I could just take photos as I drifted along. If we go back to Iceland we will definitely be doing this again. No fish to be seen, but the fissure was still amazing.
This tour was okay. It was definitely interesting to go into the lava tube and see the many different textures of the walls/floor/ceiling throughout the tunnels. The helmets were a lifesaver many many times. Be prepared to crouch, bend, crawl, and roll to get through some spots in this tour.