Go Walk: Slieve Gullion, Co Armagh

When Ireland's share of molten lava was cooling down, 60 million years ago, a little bit plopped up, like boiling custard, but didn't plop down again. South Co Armagh was left with a central mountain, Slieve Gullion, surrounded by a ring of smaller mountains. This "ring dyke system" is now required viewing for geologists from around Europe.

Before the geologists, however, Slieve Gullion had already played host to witches, Ulster heroes and fleeing saints. This is the land of Táin Bó Cuailgne, Fionn Mac Cumhaill and the old hag Calliagh Berra. The silent crags also guard many a Mass stone, and it was here that Oliver Plunkett sought refuge.

The route rises quickly from Slieve Gullion Courtyard Centre through deciduous woodland and out on to open heath. A well-worn turf path rises steeply until you reach a stone shelter.

From here it's a straightforward hillwalk to the height of Slieve Gullion, at 573m, with little scrambling involved. A stone cairn built during the Victorian era marks the summit, atop a huge burial chamber constructed by Neolithic Armagh locals. Both great cairn builders, the Victorians and the Neolithics, separated by some 3,000 years.

This vantage point gives you the geologist's view of the rest of the Ring of Gullion and the poet's view of the Mourne Mountains sweeping down to the sea.

Of course, if it's a fine soft day bucketing down - with the only view your hand in front of your face - you could content yourself with searching for the slowest-growing things on earth: lichens. The most common, looking like white splodges on the granite boulders, are dog's tooth lichens. But look carefully and you might see specimens from the genus Haematomma: the blood-drop lichens. Pale green with blood-red drops, these grow about a quarter of a centimetre in 100 years.

The summit ridge leads down to Calliagh Berra's Lough. Several legends attach to this lake - this, after all, is the home territory of Táin Bó Cuailgne. The warrior Fionn Mac Cumhaill was lured into the pool, emerging as a wizened, white-haired old man. His friends dug into the cairn on Slieve Gullion to find the Calliagh Berra, the witch who caused the enchantment. She restored Fionn, but his former head of red hair remained white.

No wonder the writer CS Lewis wandered these mountains looking for inspiration. It makes you wonder: are we in the area of "the garden and magic tree which lie to the west of Narnia, at the end of the blue lake"?

From here it's all downhill. The odd metal arrow points the way to the official Ring of Gullion Way, which leads back, via the old Killevy Church, to Slieve Gullion Courtyard Centre.