Bothwell Castle is one of over 30 top Historic Scotland attractions taking part across the country, dramatically located by a winding curve in the River Clyde.
The magnificent medieval castle also passed back and forth between English and Scottish hands during the Wars of Independence.
Free ticket registration began at www.ticketgiveaway.co.uk on Tuesday.
On Thursday, November 28, members of the general public will have until 5 pm to register online to apply for tickets to the attraction they want.
Tickets can only be exchanged during the weekend of the Ticket Giveaway. Just Saturday, 30 November, the Blackhouse, Arnol and Iona Abbey will be open.
Up to two adults and three children are permitted per site and visitors are required to pre-book Edinburgh Castle, Stirling Castle, Doune Castle and Maeshowe timeslots.
The campaign this year was launched at Jedburgh Abbey, one of the sites participating in the giveaway, encouraging people across Scotland to take advantage of the opportunity to visit some of the most iconic attractions in the country free of charge.
Stephen Duncan, Head of Commercial and Tourism at HES, said: “I am pleased to announce details of this year’s Ticket Giveaway, which offers free admission to a host of our winter-opening ticket attractions over the weekend of St Andrew’s Day.
“We are committed to ensuring that our cultural environment is preserved and appreciated by all.
“If you’ve never been to your nearest historic site, this is your opportunity to get out and explore the amazing history of Scotland free of charge.”