It's a square tower, with a stair-turret at one angle.
The stair in that turret is in a very good state of preservation--in fact, it is quite easy to climb to the top, and from the top there's a fine view of land and sea: the Keep itself is nearly a hundred feet in height.

Now the inside of the Keep is completely gutted, as you'll presently see--there isn't a floor left of the five or six which were once there.

And I'm sorry to say there's very little protection when one's at the top--merely a narrow ledge with a very low parapet, which in places is badly broken.

Consequently, any one who climbs to the top must be very careful, or there's the danger of slipping off that ledge and falling to the bottom.

Now in my opinion that's precisely what happened on Sunday afternoon.