EXPERTS are currently examining a secret tunnel unearthed in the Tirydail area of Ammanford, the Guardian has learnt.
Although the precise location is being kept secret, it is understood the underground passage was found in the vicinity of Ammanford's overgrown motte and bailey castle at the weekend.
A tight security cordon has been thrown around the site and burly guards wearing reflective jackets are turning away would-be curiosity seekers and sightseers "on health and safety grounds".
Members of the Dyfed Archaelogical Trust are believed to be inspecting an apparent exit point near Myddynfych Farm just under a mile away.
One source claimed the tunnel was found by construction workers laying foundations for the planned Gwynfryn extra care home in Tirydail.
"They initially thought it was an old sewer – but quickly realised it something else," he said.
According to local legend, a secret tunnel extends all the way from Ammanford Castle to Carreg Cennen Castle in Llandeilo.
The source added: "This is an amazing find which gives us a fascinating glimpse into Ammanford's medieval past."
A Carmarthenshire County Council spokeswoman declined to comment on suggestions that the discovery would delay plans for the £2m Gwynfryn home.
More details are expected to be revealed at a press conference at nearby Coleg Sir Gar at 12 noon today (April 1), after the Guardian's print edition has gone to press.
Guardian editor Mike Lewis writes: "Before any of our online viewers feel compelled to grab their pick and shovels and dust off any old miners' helmets that may be lying around, they should first remember today's date!"