Visited 17.07.13
It was third time lucky on the MV Glorious out of Girvan. We were turned back by the waves on two previous trips but persistence rewarded me with around two hours on the rock.
The rock has a lighthouse, two foghorns, a ruined tower house and industrial remains on the shore. It is famous for Ailsite granite curling stones which are prized for their durability. Some unshaped stones can be found on the beach.
There is more vegetation than is apparent from a distance and the grassy summit is 338 metres above sea level.
Didn't realise it has a castle... must be one of the best sited in all Scotland
As you say its probably more like a castle for defensive purposes. I've added a picture to the site.
Of course... all Olympic Curling Stones have been and are made from Ailsa Craig Granite. The stones are all still hand-made in Ayrshire. I have a very old one in my rockery!
It is about thirty five years since I've been out on Ailsa Craig but I remember some quite big caves along the shoreline. Stone coffins were found in one of them, resting places for the late occupants of the Medieval Tower House.