Yorkshire's 'stealth' heritage: The hidden monuments that many people don't know exist

York Guildhall, with the door to the hidden  passageway Common Hall Lane visible just above the water line
York Guildhall, with the door to the hidden passageway Common Hall Lane visible just above the water line
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"It's like the world's greatest detective story just laid out in front of you."

Historic England's inspector of ancient monuments Neil Redfern is referring to the satisfaction of discovering hidden history beneath our noses.

Inside Pontefract's underground hermitage

Inside Pontefract's underground hermitage

He is in charge of finding preserved clues to our past in the most unlikely of places so that they can be listed and protected by the heritage body.

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Whether that's the remains of a medieval hermitage beneath a road in Pontefract, the last surviving part of Scarborough's city walls in a car park, or the sites of World War Two 'decoy defences' in the North York Moors that sound like a Dad's Army plot, Yorkshire is full of 'stealth' heritage that most of use don't know exists.

"There are some real gems. To sustain our heritage values, we have to be curious about everyday things around us, ask questions and get a good story out of them."

The medieval hermitage beneath a 19th-century dispensary

A 19th-century statue of a skeleton doing a death dance in the Pontefract hermitage

A 19th-century statue of a skeleton doing a death dance in the Pontefract hermitage

These 14th-century chambers hewn from rock where a hermit once lived still exist underneath a road in Pontefract.

Access is via the old Pontefract General Infirmary, which was built as the town's dispensary in 1812 and which is still in NHS ownership.

The hermitage was carved out of sandstone and has two chambers on different levels. There is also a spiral staircase that leads to a well. One chamber, the Oratory, contains a fireplace, stool, bench, bed shelf and 19th-century brick pier. The staircase has 72 steps and there is a statue of Death, a skeleton carrying a spear. There are three 19th-century doorways to provide security for the well, as it was thought to contain holy water that could be taken for witchcraft.

It was discovered in the 19th century by workmen who literally 'fell into it', according to Neil.

A monk from Ampleforth Abbey surveys the remains of the beech avenue at Gilling Castle, which was felled in the 1940s

A monk from Ampleforth Abbey surveys the remains of the beech avenue at Gilling Castle, which was felled in the 1940s

"It's an extraordinary place. There is a group who look after it and they do an amazing job. Access is difficult - the dispensary was built over the area and there is no general public access. A flower planter used to mark the location underneath the road! They do hold open days for visitors."

The Roman road underneath York Guildhall

York's 14th-century Guildhall is currently undergoing restoration - and Historic England hope the project will see the public given access to Common Hall Lane for the first time.

The building and medieval lane were constructed over the likely route of the Roman road that led from Stonegate down to the crossing and wharves of the River Ouse. Now an enclosed passageway, it's hidden behind an inauspicious wooden door and prone to flooding.

Thornborough Henges, with the most northerly henge concealed by woodland

Thornborough Henges, with the most northerly henge concealed by woodland

"Common Hall Lane is a brilliant story. It forms a direct line from Stonegate, the principal Roman road, down to the river. The stone used to build the Minster was probably landed there. You can easily walk past the wooden door without noticing it.

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"If you go to North Street Gardens, on the far bank, and look back across, you can see the door at the other end on the riverside frontage."

The mirror that was used as a WW1 coastal defence

The acoustic mirror on the Yorkshire coast at Kilnsea is the legacy of a scientific experiment that never really took off.

It was installed in 1918 to protect Hull and the Humber Estuary from German air and sea attacks. The basic sound technology enabled a 'listener' to detect the vibrations from approaching aircraft and vessels and transmit an early warning. A chain of similar devices was strung across the north-east coast, but little is known about the project and the war ended soon after they had been built.

By 1936, the rudimentary technology had become obsolete and was replaced by radar in time for World War Two, although the Yorkshire coast continued to be the site of numerous detection stations and listening posts.

The site of Skipsea Castle

The site of Skipsea Castle

The Grade II-listed concrete bowl still has an entrance to the underground bunker where the operator would have worked.

"The sound mirror is amazing. It was a very early radar method, and it just sits out in a field overlooking the sea. It has great aesthetic value, but as it's such a huge lump of concrete, it's never been worth the effort of removing it."

Traces of the lost gardens that once surrounded a country mansion

Gilling Castle in North Yorkshire was the country home of the Fairfax family, who also owned Fairfax House, a York townhouse. The castle was built in the 14th century and remodelled using the original ground floor as a foundation in the 1700s.

In 1929, the castle was sold to Ampleforth Abbey, who ran a prep school attached to Ampleforth College there until 2018, and retain ownership of it today.

But a series of tantalising clues to the castle's prominent past can be found in what was once its formal landscaped gardens. The site is now Foresty Commission-owned woodland called Yearsley Woods, and it is open to the public.

"Gilling once had this amazing designed landscape. There were tree avenues, romantic ponds, exotic plant species. After the war, it became a conifer plantation, but you can still see the original paths and a series of lakes. If you look carefully, you can still spot some of the specimens, such as rhododendron.

"A Friends group are helping to restore some of the original features, but most people walking their dogs won't realise what it used to be. It's a mythical place."

The last remaining section of Scarborough's town walls - in a car park

Scarborough was once a walled town, and an important coastal fortress centred around the castle on the headland. Nobody knows exactly when the walls were pulled down, but the last remaining section of them can be found at the back of a car park on Castle Road. A blue plaque commemorates its significance.

"Scarborough underwent a lot of change after the war with slum clearances etc, so that could be how it ended up in this position. There's also a former Victorian public toilet on Albert Road that's been converted into a holiday let!"

The magic of the Bronze Age earthwork hidden in the woods

Thornborough Henges are an unusual complex of three linked Neolithic or Bronze Age monuments near Masham that probably had ritual significance. They've been called 'the Stonehenge of the north'.

Although the Central and Southern henges are the most visible of the three, they're also in a poorer condition than the better-preserved Northern henge - which is concealed in woodland.

"They're the second-highest earth banks of any henge in the country and they are an amazing sight. There is public access into the woods where the Northern henge is and it's the most evocative of places."

The secret castles

Skipsea Castle was a Norman motte and bailey castle built to deter Danish invasion and as the principal residence of the first Lord of Holderness. It was surrounded by Skipsea Mere, an artificial lake that was linked to the sea via a navigable channel. It was destroyed in the 13th century when its owned rebelled against the Crown, and the mere was also drained during the medieval period.

The castle mound - the motte - survives in open countryside; coastal erosion means that it is now less than two miles from the sea. Two years ago, a team of archaeologists drilled boreholes in the motte and uncovered organic matter dating back to 400BC, suggesting the site had earlier origins.

"Skipsea was once an inland port - you could sail all the way to the castle's harbour. The coastline has changed a lot since then. In 2017, some students from Reading University drilled boreholes into the motte, and we now believe it was previously a Bronze Age barrow.

"It's important as it shows the Normans didn't just build castles from scratch - they chose prominent locations that may have already been in use as defences. The motte now is in open countryside and there is free access."

Another hidden motte is the remains of Hood Hill Castle in the North York Moors - one of a chain of defences along the western edge of the Vale of York that also included Crayke, Sheriff Hutton and Walton castles.

"It's in some Foresty Commission woodland near the White Horse of Kilburn. It's quite a steep walk up there. It's covered in trees and there is no signage at the site."

The fake WW2 airfields designed to fool Nazi bomber crews

Despite their remote location, the North York Moors saw a surprising amount of defensive activity during World War Two.

The circular pit that once contained an an anti-aircraft gun emplacement remains at Roulston Scar, the plateau which has been used as a glider station for decades. It was feared that German men who had been sent for flying training at the site before the war would use it as a landmark to navigate by when piloting Luftwaffe bombers.

At Garbutt Farm, near the National Park visitor centre, are the remains of several shelters from the period that tell the story of one of the strangest acts of subterfuge sanctioned by the wartime government.

It was a decoy site - a fake airfield intended to distract Nazi bomber crews from the real targets.

"From there, you could see all of the airfields in the Vale of York. The RAF set up fake airfields and this was the control centre - it's a scheduled monument."

These installations often had inflatable planes and buildings, while they could also 'mirror' bombs being dropped and would shine deceptive lights.

"They were trying to attract the bombers. They mimicked lights - one of them was meant to look like the sparks from a tram, but it was just a man on a bicycle towing a lamp behind him! Once the bombs were dropped, they could set fires so that it looked as if the raid had been successful."

There were similar decoys at Sunk Island near Hull - which was designed to deflect attention from the city's docks - and Snainton Moor, which was meant to imitate Middlesbrough.

"Snainton Moor still has the huge earth banks that were used to keep the fires under control."