Thousands of Outlander fans have swamped the website of Scotland’s national heritage body after it announced a ticket giveaway allowing people to visit some of the series’ most iconic filming locations for free.

Historic Environment Scotland (HES) revealed plans to throw open the doors of sites including Edinburgh Castle, Stirling Castle and Arbroath Abbey across St Andrew’s Day weekend in an effort to encourage those across the country to explore Scotland’s history earlier this month.

However, the ballot for free tickets has created a surge in demand for fans of the popular time-travelling romantic adventure series after a number of instantly recognisable backdrops for the show were announced as part of the deal.

READ MORE: Everything you need to know about hit TV show Outlander

Thousands of fans have now tried to register for free tickets to the sites, including Linlithgow Palace, which features as the infamous Wentworth Prison.

The show, based on the bestselling books by US author Diana Gabaldon, charts the adventures of former combat nurse Claire Fraser, played by Caitriona Balfe, who is transported back in time to 1743 where she meets Highland warrior Jamie Fraser, portrayed by Sam Heughan.

HeraldScotland: Doune Castle is one of several Scottish sites featured in the show to be opened up on St Andrew's Day weekendDoune Castle is one of several Scottish sites featured in the show to be opened up on St Andrew's Day weekend

Blackness Castle, which plays the part of Fort William, Craigmillar Castle, used as the setting for Ardmuir Prison in series three and Doune Castle, which serves as Castle Leoch in the show, are also set to be opened to the public as part of the weekend.

The ballot remains open until 5pm on Thursday, November 28, but a limited number of tickets have been made available for free.

READ MORE: Outlander star Catriona Balfe spotted filming on the streets of Paisley

Stephen Duncan, director of commercial and tourism at HES, said: “We’re committed to ensuring that everyone has the opportunity to explore and enjoy our historic environment.”

“If you’ve never visited your local historic site, this is your chance to get out and discover Scotland’s fascinating past for free.”

Details on the ticket giveaway can be found here.