They were built to ward off the threat of invasion in the darkest days of the Second World War - and now a pair of pillboxes are being opened to the public.

Two restored defensive structures at Sheringham Park will go on show as part of the National Trust's Heritage Open Days.

A spokesperson said: "These were part of the defences of this section of the coast.

Eastern Daily Press: National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days.National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days. (Image: PA / Joe Giddens)

"Two slightly different designs can be seen in conjunction with other nearby defensive structures. These, along with maps of the complete defensive layouts, enable a good understanding of the plan of defence."

Around 18,000 pillboxes were built around the British coastline during the Second World War.

Eastern Daily Press: National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days.National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days. (Image: PA / Joe Giddens)

The pillboxes will be open on Thursday (September 16) and Friday from 11am-4pm. Bookings are not required.

Heritage Open Days events are taking place across the county.

There are more than 300 free events happening including walks, performances and tours.

visit www.heritageopendays.org.uk to find out more.

Eastern Daily Press: National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days.National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days. (Image: PA / Joe Giddens)

Eastern Daily Press: National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days.National Trust assistant ranger Rupert Eris dressed in Home Guard uniform at one of two restored WWII pillboxes in Sheringham Park, Norfolk, which are being opened to the public as part of the National Trust's Heritage Open Days. (Image: PA / Joe Giddens)