From undiscovered gardens to magnificent castles, Kent is full of history. And this weekend, thanks to Heritage Open Days, you can explore some of the best bits for FREE.

Until Sunday, September 14, hundreds of buildings will be welcoming visitors all across the county. We've found six of the best - but for a full list of what's open - and when - go to www.heritageopendays.org.uk

Tonbridge boasts Kent’s best example of a Motte-and-Bailey gatehouse and this weekend the castle’s colourful story can be uncovered. Built in 1086, the impressive site still watches over the town and has been recently re-roofed with new interior lighting to offer partial tours of its gatehouse throughout the weekend. Just outside on the castle lawn, the annual Tonbridge Castle Medieval Fair will take place from 10am to 5pm on Saturday, September 13 and Sunday, September 14. Offering all the usual excitement of life in 15th-century England, knights, jesters and displays of 600-year-old crafts are set to draw the crowds.

Visit www.tonbridgecastle.org or call 01732 770929

A glorious landmark building on the seafront between Whitstable and Tankerton, the castle is offering guided tours this Saturday, September 13. Formerly a Victorian family home, it now has three acres of landscaped gardens, a wonderful pirate playground for children, and tearooms. There’s great views from the roof terrace across Whitstable harbour to the estuary. The tours will run every 90 minutes, starting from the castle’s reception.

Visit www.whitstablecastle.co.uk or call 01227 281726

GRAND SHAFT STAIRCASE

Hidden inside Dover’s iconic White Cliffs sits the equally impressive Grand Shaft. If the kids love exploring, they’ll love the rare triple spiral staircase which was built between 1803 and 1809 to connect the Grand Shaft barracks on the cliff top with Snargate Street at sea level. The rarely opened site has hundreds of steps – so be prepared for a climb. However, the views from the top that stretch across the Channel are well worth the effort. The Grand Shaft is open across the weekend from 10am to 4pm.

Visit www.doverwesternheights.org

THEATRE ROYAL MARGATE

If you’ve always wondered what it’s like to sit in a royal box, you can do just that at Margate’s Theatre Royal this weekend. Dating back to 1787 and remodelled by the Victorians, the Theatre Royal is proud to be the second oldest working theatre in the UK and has masses of history to explore. It is opening its doors for the whole weekend so visitors can check out the view from the best seats and soak up the historic atmosphere of this gem of a theatre.

Visit www.theatreroyalmargate.com

COMMISSIONER’S GARDEN, CHATHAM

Nestled behind the ships at the Historic Dockyard Chatham is the open space of Commissioner’s Garden. The elegant, relatively unexplored garden sits behind the oldest naval building in Britain and has a wealth of untold stories to tell. Organisers are putting on tours across the weekend where visitors will be led through both the garden and Edwardian greenhouse. The tours need to be pre-booked but are free. They last about one hour and are available on Saturday, September 13, and Sunday, September 14. Normal admission prices apply to all other galleries and attractions.

Visit www.thedockyard.co.uk or call 01634 823852

COBHAM MAUSOLEUM

It only opened to the public in April and now the Darnley Mausoleum at Cobham, near Gravesend, is gearing up for an open day. The 18th-century monument is set in woodland and was once part of the extensive Cobham Hall estate. The mausoleum was acquired by the National Trust last year and volunteers will be on hand this Sunday at the nearby South Lodge Barn from 11am to 5pm to explain the fascinating restoration.

Visit nationaltrust.org.uk/cobham-wood

Heritage Open Days are your once-a-year chance to explore the world on your doorstep, unlocked and completely free of charge. Open days start on Thursday, September 11 and run until Sunday, September 14 across the county. Visit www.heritageopendays.org.uk for details.