A mysterious ancient underground archway that was found by workmen carrying out improvement works in Abergavenny’s St John’s Square prior to the 2016 Eisteddfod baffled local people and those working on the site.

The renovation of the square was part of the million-pound facelift set to revitalise Abergavenny.

The significant revamp transformed the Square into the pedestrian-friendly seating area we all know, love and drink beer and coffee in.

But back then, while the diggers were busy digging and the workmen busy whistling, they unearthed a mysterious archway about five feet underground, which was probably not a portal into another dimension, but nevertheless, looked pretty impressive and strikingly historic.

Work was immediately halted in the wake of the surprise find and Monmouthshire County Council was contacted to determine if the arch was of archeological importance.

The Site Manager informed Monmouthshire County Council who in turn instructed him to backfill the hole.

The site’s clerk of works believed the archway could be an entranceway to a cellar or possibly a culvert, but little else. The rest of Abergavenny was not so sure.

Rumours have long circulated in the town, that there exists an underground tunnel network in Abergavenny which begins at the castle and leads to St. Mary’s Priory Church.

Had the hard-hatted workers accidentally discovered one such archway that leads to a medieval maze of Machiavellian intrigue?

Or perhaps the mysterious archway merely led to a long abandoned cellar, belonging to one of the many Elizabethan houses that once littered the area.

Like much of old Abergavenny they were systematically destroyed during the town’s slum clearances in the 1950/60s which transformed Tudor Street and St John’s Square beyond all recognition.

The more adventurous suggested it led to an underground network of tunnels once used by none other than the legendary Prince of Wales Owain Glyndwr, who guided his troops through the dark and winding maze to breach Abergavenny’s walls and plunder the poor old unsuspecting mother duck senseless in 1404.

Yet others have suggested they were used by the Brotherhood of monks at St. Mary’s for all sorts of shady and sinister purposes.

There were even fantastical suggestions that the underground arch formed part of an entrance to a dungeon once used by the now-defunct Chevron nightclub to dump their more rowdy clientele until they had a chance to sober up.

Some even claimed the archway was a secret portal to the labyrinth of a supernatural and terrible beast-like creature which had lied dormant beneath the Gateway to Wales for centuries, but which was now awoken by the inferno of modern machinery and men in high-vis jackets.

Many feared that unwisely prodding this foul scourge of centuries, was like hitting a grumpy bear with a big stick, and might just cause it to rise from its slothful slumber and go berserk in time for the National Eisteddfod.

As theories go, most of the above are pushing the envelope somewhat but the existence of an ancient tunnel network beneath the street of old mother Abergavenny stirred something timeless in our modern souls - the obsession with that which lies beneath.

Our fascination with underground spaces and passageways is as old as the hills. They loom large in our psyche as dark and remote portals to an otherworld where magic and wonder hold sway.

Underground spaces are one of the few areas left on this spinning rock we call home which remains untouched, untainted, and unshackled by civilisation.

The Abergavenny tunnels are now considered something of an urban myth, but rewind a few decades and many locals appeared to take their existence for granted but thought it was no big deal.

For example, many castles scattered across the UK contained underground tunnels that led to the outskirts of the town. The nobles could disappear into these in case of a prolonged siege.

A short escape tunnel was located at Loundon Castle in Ayrshire. Scotland and in 1330 a group of troops loyal to Edward III took advantage of a secret tunnel to take Nottingham Castle by surprise and liberate the imprisoned king who was being held captive by Roger de Mortimer, 1st Earl of March.

Closer to home, in the 1950s a tunnel filled with water was found in the basement of The Angel Hotel in Cardiff was said to have connected directly to the castle, whose own tunnels were used as air-raid shelters during the Second World War.

Although Llandudno is best known as a popular seaside resort, in certain quarters it is also renowned for its lost tunnel network which spans miles and in some instances leads out into the ocean.

The tunnels were part of a 19th-century copper mine.

For the best part of four decades, the Great Orme Exploration Society (GOES) has been working to open up the tunnels in the mine to the general public.

The entrance to the tunnels are hidden by a bog standard steel manhole close to Llandudno Pier.

Their dream looks set to soon become a reality with GOES coordinator Adrian Hughes telling The Daily Post at the tail-end of 2023, “It will open up a whole new subterranean world to us. We’ve long known there are more tunnels and gaining access to them was one of the main aims of the society when it was founded.”

In picturesque Tenby, an old chamber that still exists in a present day’s chemist’s shop leads to a network of tunnels that access the harbour.

Local legend has it that these tunnels were used by the future Tudor King Henry VIII when he was fleeing the murderous intent of King Richard III and his English army.

In 2012 Dewi Prysor featured the Tenby tunnels on S4C show Darn Bach o Hanes (A Bit Of History). He later told The Western Telegraph that in Tenby, “Apart from the Norman walls and castle that were built to keep out Welsh forces, the only medieval buildings left are a striking Tudor House, which is now run as a museum by the National Trust, and the ancient St Mary’s Church.

“But underneath the town, there is a labyrinth of fascinating tunnels.”

So if other sites of historic interest in the UK have a network of tunnels, why not Abergavenny?

Although there are no written records or plans to confirm their whereabouts, there is a strong oral tradition in the town that aforesaid tunnels do exist.

In his book Historical Notes On Abergavenny, the author John G. Williams writes, “One such tunnel is supposed to pass under Nevill Street and then down Frogmore Street, and some years ago signs of this were discovered at No. 61 Frogmore Street when it was in the occupation of Mr. Owen, the Chemist. Another tunnel seems to have been in the Cross Street area as some time before 1939 one of my friends remembers a motor car being driven under the archway at the King’s Head Inn when the ground underneath it, near the old stables, fell in and revealed an underground tunnel that was partly filed in. Farther down the street the remains of a tunnel were discovered when workmen were excavating to build the underground strongroom for the present site of Lloyds Bank Ltd. These might be the remains of a tunnel from the Castle to the Priory Church, and I have heard that this tunnel is supposed to travel as far as the very old farmhouse called Wernddu in Llantilio Pertholey and adjoining the Abergavenny to Ross Road.”

In 2017 a photographer uncovered a stunning 700-year-old underground complex in Shifnal, Shropshire known as the Caynton Caves. The entrance to this subterranean world looked barely bigger than a rabbit hole and was apparently used by the Knights Templar.

Apparently, the Knights Templar were said to have been fans of tunnels in a big way.

There’s not any documented evidence of Knights Templar activity in Abergavenny but there is an effigy of Sir John De Hastings in St. Mary’s Church.

The effigy of Hastings is carved cross-legged and this was once thought to imply that the deceased had served in the Crusades, had taken crusading vows, or more specifically had been a Knight Templar.

Hastings acquired Abergavenny Castle and significantly contributed to the 14th-century rebuilding of the Priory. What better opportunity to build a tunnel network between the two?

Monmouthshire County Council did eventually get to the bottom of the mysterious archway in St. John’s Square.

A spokesperson for the authority said, “Whilst undertaking excavation works to plant trees in St John's Square, our contractor uncovered an underground structure which appeared to be a cellar.

“To make the area safe, the excavated void was filled with soft excavated material. Examination of the historic maps indicated that there was a row of houses and, in particular, a public house at or near this location. These properties were demolished circa 1960.

“It seems most likely that the structure is the cellar of the public house which formerly occupied the site.”

So there we have it. The archway that got everyone gossiping was probably a pub cellar, but the wider mystery of Abergavenny’s network of tunnels rumbles on. All anyone can hope to do is follow the white rabbit and get digging!

Because, as recently as 2021 a network of medieval tunnels was found elsewhere in Monmouthshire when a group of electrical contractors accidentally found an underground network in a local resident’s back garden.

Whilst digging up the ground nearby a fast-flowing stream to install some underground cabling, the team from Western Power Distribution (WPD) accidentally unearthed what was obviously a man-made passage, four feet in height and very mysterious.

Technician Allyn Gore told Wales Online, “Before work began we'd done all the usual checks and nothing had shown up on any of our drawings or records to indicate there was anything unusual about the site.

"But shortly after the excavation began, the digging team made the extraordinary discovery of what they initially thought to be a cave.

Allyn added, "Work stopped immediately and we were called in to decide what course of action we should take next.

"I have previously been involved in other excavations where we've discovered old wells and cellars not shown on any plans, but nothing as exciting and impressive as this."

A man from Cadw was called and the decision was made in the interests of public safety to fill in the passage before any serious archeological investigation could take place.

Allyn explained, “We backfilled the trench and reinstated everything because it could take years before any investigations are concluded."

Did the tunnels have any connection to the nearby Tintern Abbey, or was there some other weird and wonderful reason for their existence? In time we may find out, but then again we may not.

Meanwhile, let’s end with one of the most curious underground lairs to ever grace Wales.

During the Second World War, London was suffering repeated bombings from the Luftwaffe and there was a real fear that priceless artefacts and artworks from antiquity were at risk of being lost as the Blitz reduced more and more buildings to rubble and memory.

In a bid to preserve these priceless items, the British Museum transferred many of them to the National Library of Wales in Aberystwyth where architect Charles Holden was given the brief to design a tunnel that could be dug out of a rock outcrop near the main building to house them all in.

From July 18, 1940, to May 23, 1945, the Magna Carta, William Shakespeare manuscripts, Leonardo da Vinci drawings, paintings by Rembrandt, and letters written by the kings and queens of England were just some of the 100 tones of items that the British Museum placed in these curious tunnels.

A scholar named Victor Scholderer was so concerned that the air conditioning might break down and damage their precious trove of treasure he slept in the tunnels with his colleagues.

It’s doubtful that anything so bizarre or intriguing lies in the rumoured network of tunnels beneath Abergavenny, but all that hides in the dark will one day be exposed by the light!