The new trail leading to Ireland's mythical 'Gate to Hell'

Rathcroghan is one of Europe's oldest unexcavated royal sites. Now, a brand-new walking path is giving travellers access to ancient landmarks – including the cave that inspired Halloween.

From the top of Rathcroghan Mound in Ireland's County Roscommon, the view stretches across grassy fields, stone walls and grazing cattle and sheep. While this may appear as unassuming farmland, a closer look reveals dozens of large, circular earthworks and ancient burial mounds.

That's because Rathcroghan (meaning "the fort of Cruachan" in Irish) is one of the oldest and largest unexcavated royal sites in Europe. This was the ancient capital of Ireland's Connacht province and 266 archaeological relics are spread across the 6.5sq-km site – including Iron Age ringforts, Ogham stones carved with ancient Irish script and holy wells.

But one of Rathcroghan's most mysterious features is a passageway that extends deep into the earth and crosses the mythological veil into the Celtic Otherworld. Known as Ireland's "Gate to Hell", it is considered to be the birthplace of ancient traditions that evolved into Halloween.

"It's a fascinating place – not many sites can claim an entrance to the Otherworld," says John Waddell, emeritus professor of archaeology at the University of Galway.

Since many of Rathcroghan's monuments are located on private farmland, visitors have historically only been able to access some of its sites by car. But a brand-new 13km (8-mile) Rathcroghan Archaeological Walking Trail now links the complex's main highlights on a looped walking path, giving travellers new access to the land and a different perspective on how these ancient monuments were connected.

A sacred, supernatural past

Rathcroghan's history stretches back 5,500 years. It was an important hub for ceremonial assemblies, as well asfeasts, seasonal celebrations and royal inaugurations.

The site has inspired a wealth of folklore. This is where Ireland's national epic, The Táin – Táin Bó Cúailnge ("The Cattle Raid of Cooley") begins and ends. Considered Ireland's version of The Iliad, it recalls a great raid started by Queen Medb of Connacht, an Iron Age warrior who ruled from her nearby palace.

"[Rathcroghan is] an ancient royal site, we're not talking about a palace being stuck out on the landscape; we're talking about a site where people came to gather for various reasons – to mark a celebration, the cross-quarter festivals, a marriage, a contract, a death, a funeral, crowning a king," says Rathcroghan tour guide and research assistant Elaine Conroy.

It's also sacred ground. The complex is considered one of the three chief burial places in ancient Ireland where the nation's early kings and chiefs were laid to rest, and today it's home to 40 identified burial mounds.

Roughly 1km south-west of the main Rathcroghan mound lies Oweynagat cave – believed to have been the home of the Mórrígan, the supernatural goddess associated with the birth of Halloween. The deity appears as a shape-shifter in The Táin and is associated with the festival of........

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