One of the most unique activities you can do on a visit to Iceland is to do a glacier hike and ice cave visit. Glaciers are shrinking every year so see them now to enjoy them at the current state while you can. There are many glacier hike and ice cave visit tours available – going with a guide is a must as they have the experience to keep you safe. Tours are also highly dependent on weather, and the ice caves with the beautiful blue ice generally are accessible starting in fall through spring and not during the summer. That said there are some caves accessible in the summer as well – just with less blue. Our visit was in mid-October, and although the sun did not come out until later, we were still able to admire the unique blues of the ice even in the overcast sky and were grateful it wasn’t raining or snowing and not too windy either.
The farther you get from Reykjavik the better the ice caves will likely be – so pay attention to where your tour will start and go, and if possible which outlet glacier. The marketing names for the ice caves, ranging from “Crystal Blue” to “Sapphire” or “Blue Ice” variations, make it hard to differentiate, and some require hiking in, others use a super jeep or snowmobile or other vehicle to reduce walking. The amount of time or size of the cave varies not just from cave to cave but also every year.
One of the ice caves on Langjökull Glacier is a manmade cave that is more of a tunnel. I think the natural glacier caves on Vatnajökull are preferable, though many more hours away versus easily do-able from Reykjavik. You probably want an ice cave of Vatnajökull, Europe’s largest glacier, covering 10% of Iceland, and which has around 30 outlet glaciers. My impression is that the glacier hike and ice cave visit tours that leave from Jökulsárlón are larger ice caves then from Skaftafell or the ones on Katla from Vik. I also believe the Katla ice caves have less blue and more black ice from being part of Katla volcano. You will likely need to stay overnight somewhere in the Southeast coast the day before your hike in order to do the tours on Vatnajökull.
The tour we went with Troll Expeditions was a glacier hike and ice cave visit from the Skaftafell Terminal. We hiked to the glacier past initial areas of volcanic and mossy fields so viewed the green moss landscape up close and the glacier from afar before actually walking on the glacier ice itself. Don’t walk on precious moss. Moss is slow growing (1 cm each year), and has short roots, so walking on the fragile moss can pull it up and kill it, and it take decades or even centuries to grow back. Moss could also be hiding sharp edges or crevices or holes in the lava field. So only visually enjoy the moss fields and stay on the trails.
Of the 4 hour tour, probably about an hour was spent being fitted for our crampons and getting other gear like a helmet with headlamp, harness, and ice axe; driving to and where we were dropped off to start our hike; and returning our equipment. So about 3 hours of actual physical activity, and maybe 20 min actually in the ice cave. Our group was broken into two so half of us (we were in the first group of 9 of us, total group size for the tour was about a 15 people) entered first as it is a small cave. Then we switched where we exited and then toured and hiked the glacier with one of the two guides.