This is without a doubt the best thing I did in my recent visit to Iceland. The guides were heaps of fun and gave great commentary on the drive there. When we arrived at Silfra, we were given a very good rundown of how the dive would go, what we'd see, a bit of history and then a rundown on how to use the equipment (none of us had used dry-suits before).
The equipment provided was top notch. I loved having a decent mask and fins for a change. And the dry-suit kept me dry and warm (with the help of my 2 sets of thermals - I highly recommend this). They provide hot chocolate and cookies while they change tanks.
We did 2 dives. The clarity is unbelievable - 100m+. I had a bit of a drink 10m down - the water tastes amazing! The blue is spectacular.
This dive is going to be one I'll always remember - especially with the amazing photos the guide took of us.