Clontarf is named after a famous battleground and fashionable watering-place near Dublin, Ireland. In 1868 a son of Queen Victoria was shot in the back by an Irishman here. Oh, the karma.
The Prince gave his name to a hospital and apparently a Norfolk Island pine, planted to mark the place where the Duke was shot, still exists in Holmes Avenue (PDF).
Clontarf has been a Pleasure Grounds (“quoits, skittles, cricket bats &c always kept on the ground”) and a tent city during the Depression.
The point itself is just a couple of steps off The Spit to Manly scenic walk and it’s worth taking in the view.