At a time when everything seems to have a price tag, it’s rare to find a decent day out that can be enjoyed for free. Celebrating its 30th anniversary this year, the week-long Heritage Open Days festival provides members of the public with an opportunity to sneak behind secret doorways and have exclusive one-off tours of popular sites – all without spending a penny.

This year, the theme is Routes – Networks – Connections, celebrating how people and ideas have moved around and come together throughout history.

There are around 5,000 different events taking place between September 6 and 15 across the UK.

Here are a few of the top picks to enjoy.

Dover College and Dover Priory, Kent

For almost 900 years, people have been chomping down in the dining hall of Dover college, which was once the Ancient Priory of St Martin. Founded in 1130, it’s the only Norman refectory in the world still used for its original purpose.

Throughout the centuries, it’s provided an important backdrop for various historical events: King Stephen died here in 1154 on his way back from France, and the Bayeux Tapestry was supposedly hung from walls. Years later, it featured in one of Turner’s famous paintings after Dover college opened on the site of the ruins in 1871.

How: Three hour-long tours will take place on September 7 at 11am, 12pm and 1pm. Visit bookwhen.com/dovercollegemaincampus.

Blickling Estate, Norfolk

Heritage days aren’t only about peeping beyond the closed doors of buildings. Gain a behind-the-scenes insight into work being done to protect our waterways on a guided walk along the River Bure in Blickling Estate. Learn about the flora and fauna living in this rare chalk stream habitat and the restoration of floodplains and grasslands, all part of an ambitious Riverlands conservation project.

How: The guided 3km walk will take place on September 7 from 11am to 1pm. Visit nationaltrust.org.uk/visit/norfolk/blickling-estate.

The Guildhall, Bury-St-Edmunds

Little is known about the Royal Observer Corps, an unsung group of local heroes who were ‘the eyes and ears’ of the RAF during WW2’s Battle of Britain. Their Operations Room was in St Edmunds Guildhall, now a Grade 1 listed building. Once shrouded in secrecy, their story can now be shared with the public as part of a special tour.

How: Tours held on September 7 between 10am and 4pm. Visit burystedmundsguildhall.org.uk

Stretton Watermill, Chester

Built in 1351, one of the country’s best-preserved corn mills takes visitors on a journey back through 700 years of history. Join a miller to learn about how the original wooden machinery functions and have a go at milling grain. Afterwards, enjoy the surrounding area with a picnic and stroll around the mill pond and mill buildings.

How: Visit on September 8 between 1pm and 5pm. Visit westcheshiremuseums.co.uk.

Canute’s Palace and medieval wine vaults, Southampton

It’s best known as a major cruise docking destination, but during the 1270s, Southampton was at the centre of a flourishing wine trade. Rarely open to the publics, two major vaults – Quilters Vault and the 88 High Street Vault – will be open for tours for three days. Learn about excavations and visit the neighbouring recently restored ruins of Canute’s Palace, one of Southampton oldest buildings. Discover the clues archaeologists used to date the building and learn about the meaning behind its grand name.

How: Tours on September 6, 7 and 8 from 10am to 3pm. Visit heritageopendays.org.uk.

North Yorkshire Moors Railway, Yorkshire

Running through North York Moors National Park, the North Yorkshire Moors Railway celebrates the golden era of train travel. Two stations showcasing the beauty of bygone days are Pickering and Goathland, famously used as Hogsmeade Station in the first Harry Potter film. Both will be open for 45-minute guided tours. Several other special events will also be taking place, including a guided walk along the now defunct rail line between Goathland and Grosmont and a signal box demonstration.

How: Various times and dates in early September. Visit nymr.co.uk.