Greenan Castle is a 16th-century ruined tower house, around 4 kilometres southwest of Ayr. Situated at the top of a sea cliff, it was originally a promontory fort converted into a motte-and-bailey in the 12th century. In the 15th century a tower house was built by the Lords of the Isles, which later passed into the hands of the Kennedy family.
The first known defensive structure on the site was a promontory fort, probably a fortified farmstead. Four concentric curved ditches, each around 3 metres wide, cut off the headland with the exception of a single causeway to provide access. It is not known how long this settlement was occupied, but the site was re-used in the twelfth century.
Beside the tower are traces of a walled courtyard and outbuildings, probably stables and a kitchen block, as the small tower has no kitchen within its walls.
The castle passed through various members of the clan before ending up in the hands of Thomas Kennedy, Earl of Cassillis in 1766. Around this time the residential use of the castle seems to have stopped; today the structure is a ruin.
References:Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.