It involves thousands of local volunteers and organisations across the UK. Here, we look at events between Arundel and Shoreham.
A spokesperson at www.heritageopendays.org.uk said: “Stories are told, traditions explored, and histories brought to life. It’s your chance to see hidden places and try out new experiences – and it’s all free.”

5. Marlipins Museum
Marlipins Museum, in High Street, Shoreham, is a Grade II listed Norman building, famous for its striking flint and limestone chequerboard façade. Tours available on Sunday, September 8 and 15. Pre-booking not required. Photo: Steve Robards SR1812129

6. Shoreham Fort
Heritage Open Day tours will be available at Shoreham Fort, Forthaven, Shoreham Beach, on Friday, September 13. Pre-booking required. Volunteers at Shoreham Fort will share some of the unique and diverse history of this hidden Scheduled Monument, situated at the eastern end of the shingle spit that used to be known as Bungalow Town. Book at www.eventbrite.co.uk/e/shoreham-fort-hods-tours-tickets-891251064927 Photo: Elaine Hammond / SussexWorld

7. Old Shoreham Heritage Trail
A guided tour of St Nicolas Church, St Nicolas Lane, Shoreham, is available on September 7, 8, 14 and 15. This new Heritage Trail will be a highlight of the Old Shoreham Heritage Festival celebrating the 50th anniversary of the Conservation Area with a focus on protecting the ancient routes through this vulnerable green gap in the southern coastal strip. Pre-booking preferred at www.ticketsource.co.uk/whats-on/old-shoreham/st-nicolas-church/guided-tour-along-the-old-shoreham-heritage-trail/e-jboagg. Photo: Derek Martin

8. Who Needs Five Bridges?
Popular historian Dr Geoffrey Mead leads a walk from the Adur Ferry Bridge to the Old Shoreham Toll Bridge, starting at Coronation Green, High Street, Shoreham, at 4pm on Saturday, September 14. Pre-booking not required. Shoreham with five river crossings is surely mimicking London! Why so many? And isn’t there an obscure law about bridge spacings on a river? Photo: Eddie Mitchell