Built in the 19th Century during fears that the French could attempt to invade, Newhaven Fort is the largest work of defence ever built in Sussex.
But unlike other fortifications of the time, Newhaven Fort remained a key part of the defence of the country through both the first and second world wars.
Visitors can journey deep into its network of tunnels, venture onto its ramparts and gun emplacements and learn about the secret stories of the people who lived and worked at the fort.