Mysterious structure

Glanced out of the window and thought for a second there was a ship with a huge tower very, very close to the shore.

If this had been the case it would have been a quick call to the coast guard as the cliffs and skerries over there wouldn't be the first choice for anyone looking for a safe harbour.

Fortunately it wasn't a ship, or the conning tower of a very large submarine... any guesses as to what it may be on the horizon?

The view without the object.