Quite simply: you have to see it. Its quite a long drive from Reykjavik - approximately 5 hours - so you may wish to find a local place to stay.  The white bergs in the really blue water ( look for the seals ! )  seem unreal at first .  There's a small  snack shop at the parking area with a bathroom. Also take a walk or drive to the other side of the bridge to the black sand beach. The ocean has melted some of the bergs and the left over ones  are found in various shapes and sizes , sculpted by the wind and water.

Great photo opportunities everywhere.