My partner and I went snorkelling and caving with Arctic Adventures and thoroughly enjoyed ourselves!
I must say, the caving aspect was slightly underwhelming and I'm glad we received a discount which meant the caving part cost us very little extra on top of the snorkelling. It is quite a small cave that is just walking - no crawling, squishing or anything too adventurous. So, I guess it's good if you're after something easy!
The snorkelling, though, was something else! Freezing cold and raining, but absolutely magical! Take a towel to wrap up in afterwards (or at least for your hair which is the only part of you that gets wet because of your whole body dry suit) and lots of cosy warm clothes!
Highly highly recommend this out of world experience!