The best preserved of the castles on my list, Crookston Castle is now a Guardianship Monument in the care of Historic Scotland. The stone castle is the latest phase of occupation at the site, but it stands in a much earlier ringwork of early medieval date (c. 12th century).
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The lands of Crookston were originally owned by the de Croc family, but they were sold to Alan Stewart in 1330 and they were in the hands of the Stewarts of Darnley by the 1360s. And it was the Darnley Stewarts who were responsible for the building of the stone tower-house, which dates to the 1400’s – the two western towers were destroyed during the 1489 siege and they appear never to have been rebuilt.
Further details can be found at the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) website
And since the site is a Guardianship monument in the care of the First Minister of Scotland, it can be visited by members of the public. Full details of the location and opening times can be found by clicking on the link below:-
http://www.historic-scotland.gov.uk/propertyresults/propertydetail.htm?PropID=PL_077
Further Reading
Lewis, J, 2003. Excavations at Crookston Castle, 1973-75. Scottish Archeological Journal. Volume 25, Page 27-56 (http://www.euppublishing.com/doi/abs/10.3366/saj.2003.25.1.27)
MacGibbon, D and Ross, T 1887-92 The Castellated and Domestic Architecture of Scotland Vols 1-5 (Douglas, Edinburgh)
Tranter, N 1962-70 The Fortified House in Scotland Vols. 1-5 (Mercat Press, Edinburgh)