Reposted from the Daily Post

Today, hidden from public view and situated underground, they are the secret bunkers of another age.

But while they may largely be forgotten by the public, they have all played a vital role in the nation's history.

For buried deep under the North Wales soil, far from the UK's major cities, they have protected the nation's treasures and its deadliest secrets.

From the hiding of the Crown Jewels and Leonardo da Vinci masterpieces to storing the bouncing bomb and the development of nuclear weapons they formed a protective shield from prying eyes and devastating bombs.

So we have taken a look inside these sites of huge historical interest to look back at some of the UK government’s best kept secrets.

Beyond Manod Quary’s grey slabs of slate is a fascinating story of how millions of pounds worth of British historic masterpieces were kept safe deep underground at the height of World War II.

Across Europe treasured art was looted, bombed and burnt during the war so efforts to protect the country’s most artworks from the Nazi bombs were made by Churchill as soon as war was declared in 1939.

Among the items hidden deep in this Snowdonia mine were 19 Rembrandts, Van Dykes, Leonardo da Vincis and Gainsboroughs, as well as the Crown Jewels.

All the royal pictures from the palaces, the Tate and the National Gallery were also transported to the quarry - disguised in delivery vans for a chocolate company.

As soon as they arrived, purpose-designed squat brick “houses” were built inside the vast chambers to preserve the paintings in air-conditioned and heated safety.

Narrow gauge tracks were extended and specially designed wagons were built to carry the nation’s treasures up the steep hill from Blaenau to the mine.

Two years before the war ended, a rock fall slightly damaged five paintings, resulting in the rapid evacuation of 700 other from that part of the quarry.

After that it was regularly inspected by engineers.

The whole operation was kept top secret until it was eventually revealed after the Government’s lease on the quarry expired.

The masterpieces were returned to the walls in London as soon as peace was declared in 1945.

Manod proved to be so successful that, in the 1950s, it was the planned destination for Britain’s art treasures in the event of a third world war.

Tunnels that housed thousands of mustard gas shell during the height of production in the war years will soon be open to the public for the first time.

These former top secret tunnels at Rhydymwyn Valley Works housed thousands of mustard gas shells during the height of production during the war.

The Valley Works, which now sit in the heart of a nature reserve near Mold, were converted into a mustard gas factory by ICI on the orders of Winston Churchill.

Historians believe workers made up to 40,000 shells a week at the secret plant.

Partially due to its location near dense woodland, Rhydymwyn is the only site of its kind not discovered by the Nazi intelligence and therefore was not a target for German bombers.

But it’s role in Britain’s secret history did not end there. Amateur historians from the Rhydymwyn Valley History Society unearthed proof that the miles of tunnels also served as home to the developers of the first atomic bomb.

The site, now part of a nature reserve, finally closed in 1994 and today, it is considered historically important.

Ten years ago next summer, some of the uninspiring brick buildings were given protected status by Welsh heritage society, CADW.

Rhydymwyn tunnel tours will open to the public in 2018 for five special tours in April, May, June, July and September.

Booking is required. Visit rhydymwynvalleyhistory.co.uk to book.

As soon as World War II was declared, the dissused Glyn Rhonwy slate quarry in the heart of Snowdonia became home to a secret munitions store.

The quarry pits, equivalent to the size of two football pitches, stored around 18,000 tonnes of weapons for the duration of the war.

When an RAF airbase needed ammunition for its planes, an order would be sent through to Glyn Rhonwy and be delivered by road or by rail.

The site consisted of a number of deep open pits, linked together by tunnels.

Narrow gauge railway lines entered the lower level of the depot. It also had an underground depot and was adapted to produce a store with two floors throughout, with electric lifts transporting bombs to the upper floor.

In January 1942, two-thirds of the structure collapsed, burying 14,000 tons of bombs. The majority were recovered and although the remaining tunnels were eventually cleared of debris, no ammunition was ever stored underground at Llanberis again.

Some 30 years later in the 1970s, the site was used to dispose of old and surplus bombs, bullets and grenades.

It was confirmed that 70,000 German tabun nerve agent shells seized following World War II were held at the Llanberis quarry for a short time before they were moved to another facility near Caernarfon, and eventually dumped at sea.

A £100m hydro-electric power plant has recently been given the go head on the site, that has been disused for years.

The scheme will generate electricity by releasing water from a reservoir on higher ground to a second, lower reservoir.

Building work could begin in 2018..

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