Fionn mac Cumhaill: From the Boyne to the Giant's Causeway

The boy who will become Fionn is still called Demne when he studies near the Boyne under the poet Finnegas. Finnegas has spent seven years trying to catch a salmon that holds all knowledge, and when he finally lands it he tells the boy to cook it. Demne burns his thumb and instinctively puts it in his mouth. The wisdom passes to him, the poet gives him the whole fish and the new name Fionn, and for the rest of his life he need only bite his thumb to know what he must.

Location precision: Legend names Fec's Pool on the Boyne but no exact spot; the pin marks the river itself.

At ten, Fionn takes on Tara's yearly nightmare. For 23 years the fire-breathing Áillen has come at Samhain, lulled the city's men to sleep with his music, then burned Tara and its treasures. Fionn volunteers to guard it, borrowing a special spear, the Birga, from Fiacha mac Congha. He defeats Áillen, saves the city and is given command of the Fianna. The hill still holds the Neolithic Mound of the Hostages, built around 3,200 BC, and a standing stone believed to be the Lia Fáil.

Visitor guidance: Tara is a hilltop site near Skryne, County Meath; the Mound of the Hostages and the standing stone are among the visible monuments.

Once grown, Fionn goes to his grandfather Tadg and demands compensation for his father's death, on pain of single combat. Tadg gives up the estate of Almu, today's Hill of Allen. Legend says Fionn had a fortress here and trained his warriors on the flatlands around it. In 1859–63 a folly tower was built on the summit, and during the work a large coffin of bones came to light, said to be Fionn's. Much of the western side of the hill has since been quarried.

Location precision: Almu's identification with the Hill of Allen is traditional; the legend fixes no exact spot on the hill.

Two sisters, Áine and Milucra, both want Fionn. Knowing Áine will never marry a grey-haired man, Milucra puts a spell on the lake at the top of Slieve Gullion, then asks Fionn to fetch her golden ring from it. He emerges as an old man with grey-white hair. The Fianna force her to give him a restoring potion; his youth returns, but his hair keeps the wrong colour. In some tellings Milucra is the ancient goddess Cailleach Bhéara, and the mountain's passage grave is still called Calliagh Birra's House.

Visitor guidance: A trail leads to the summit; on the eastern side Slieve Gullion Forest Park has a visitors' centre, café and the Giant's Lair Story Trail.

Benbulben, the flat-topped mountain in County Sligo, is one of the Fianna's hunting grounds and the resting place, it is said, of Diarmuid and Gráinne. Promised to the aging Fionn, Gráinne ran off with the handsome Diarmuid. Years later Fionn invites him on a boar hunt and Diarmuid is gored. Water from Fionn's hands could heal him, but each time Fionn lets it run through his fingers on the way back. When he finally returns with it, Diarmuid has died.

Visitor guidance: The Gortarowey Looped Walk, 5.5 km and about 1.5 hours, runs alongside the mountain.

In a folk tale, Fionn scoops a chunk of earth out of Ireland and hurls it at a Scottish rival. It falls into the Irish Sea and becomes the Isle of Man, while the crater left behind fills with water and becomes Lough Neagh. The lake is the largest on the island of Ireland and in the British Isles, covering 148 square miles, and supplies 40.7% of Northern Ireland's drinking water.

Location precision: The tale names no spot on the lake; the pin marks its centre.

The Scottish giant Benandonner challenges Fionn, and Fionn builds a causeway across the North Channel so the two can meet. In a common telling he realises Benandonner is far bigger and hides, and his wife Sadhbh disguises him as a baby in a cradle. Benandonner sees the size of the "baby", imagines how huge its father must be and flees, wrecking the causeway behind him. The real site has about 40,000 interlocking basalt columns, the tallest around 12 metres, and has been a UNESCO World Heritage Site since 1986.

Visitor guidance: Access to the stones is free; you don't need to go through the visitor centre that charges a fee.

Across the sea in Scotland, identical basalt columns line Fingal's Cave on the island of Staffa, and the Causeway story may have been influenced by them. One account of the legend has Fionn building the causeway between Ireland and Scotland. The cave takes its name from the hero of James Macpherson's 18th-century epic poem, Fingal, who is Fionn mac Cumhaill in Irish mythology. Felix Mendelssohn visited in 1829 and wrote his Hebrides overture. Inside, a row of fractured columns forms a walkway just above high-water level.

Visitor guidance: Sightseeing cruises run from April to September and pass the entrance; in calm conditions some let you land on Staffa.