There are a couple of ways that you can visit Craignethan castle. It can be approached from the "Clyde valley road" (A72) which is a favourite of the "Sunday driver" due to its scenic nature and vast array of garden tea rooms leaving the main road at the small hamlet of Crossford . Alternatively it can be approached from the B7078 which runs parallel to the main motorway (M74) which links the heart of Scotland and England. Go with the B road !
After travelling down the single track for the last half mile, you will see that Craignethan Castle sits on an outcrop bordering the deep gorge of the river Nethan. It consists of a square tower house which was used as the main living, and entertaining area and in essence, is the main part of the attraction. Its fortifications are still impressive and it is protected on one side by a deep ditch in front. The further protection lies slightly further back from this with a perimeter wall with a gatehouse (now a ruin). The bridge crossing the ditch has clearly been moved from original location as the gatehouse is on the left hand side.
The castle was first built by Sir James Hamilton in 1530 and was built to defend the family from attack. However, there was never any direct military assault on the building. In fact, it was destroyed on the orders of the King and with the consent (although how freely given is open to interpretation) of Sir James, who later fell from favour and was executed for treason in 1540. Despite this timescale, the castle is remarkably complete although would still be classified as a ruin so you can allow your children to run free without the worry of them breaking anything (except for themselves of course!) .
Craignethan, like a number of other Scottish castles also has its share of ghost stories. The most important of these would be Mary Queen of Scots, who has some connection with the castle and her spectral figure has been reported to appear headless on a number of occasions including just after her execution. Other ghosts are said to haunt the castle, including a figure who is mistaken for one of the guides (dressed in period costume), only to disappear soon after.
Craignethan was later thought to be the inspiration for "Tillietudlem Castle" in Walter Scott's "Old Mortality". Scott denied that it was but at the time of writing Craignethan was covered in ivy and fitted his description perfectly. The present owners, Historic Scotland, have removed all the ivy as it damages the stonework.
Is it worth going to see? Absolutely. Wondering if it will keep the children amused - it certainly kept 3, 11 year olds happy and running around for some time. The children can play relatively safely, although you are able to access the roof of the tower which doesn't have modern safety features and is a LONG drop. Of course, parents could always exercise some responsibility.