Slieve Gullion South Cairn

The walk up Slieve Gullion rewards you with something genuinely rare - a 4,000-year-old cairn you can actually enter. Most megalithic sites are roped off and viewed from a distance, but here you'll crawl into the inner chamber itself, ducking through a narrow passage to stand where Bronze Age people once stood. The views across County Armagh from the summit aren't bad either.

It's a proper scramble to reach the South Cairn - expect forty minutes uphill from the car park near Newry, with rocky terrain that demands decent boots. The chamber itself is smaller than you'd imagine from outside, which somehow makes it more affecting. You're literally inside archaeology. The passage stones still bear tool marks from thousands of years ago.

This one's for walkers and history types rather than casual visitors. Young kids might find the steep climb tedious, though determined teenagers tend to enjoy the adventure element. Allow a full two hours for the round trip if you're taking your time.

The site sits within Slieve Gullion Forest Park, so you could easily string together a day combining this with the lake walk and picnic spots lower down. Hilltop Hideaway, just 3.6 miles away near Newry, makes a solid base if you're planning a few days exploring the Mourne foothills - that hot tub will feel earned after the climb.