Grind o' da Navir
This is, quite literally, an awesome place. A gap in the cliffs (see 1st extra) has allowed the sea to break through and excavate a large circular rocky arena. On the landward side is a huge bank of broken rocks, just visible in the distance on the right. These rocks (see 2nd extra) have been thrown 50m or more out of the arena by the sea.
Standing in the arena after scrambling over the bank of rocks, I found it almost frightening to imagine the action of the sea there during a big storm. I found this video from 2014 showing it from a safe-ish distance.
There is a lot more to see at Esha Ness - the Holes of Scraada, an inland cave linked to the sea by an underground passage; and the remains of a broch. For us, this was one of the most memorable places on Shetland.