Giant's Causeway

The first thing you notice is how many people just got off a tour bus. Then you walk down the cliff path and see the columns for the first time and understand why they all came. The Giant's Causeway — around 40,000 interlocking basalt columns, mostly hexagonal, emerging from the sea and extending inland — is one of those places where knowing the geological explanation doesn't diminish the wonder. It's a UNESCO World Heritage Site, and it earns it.

The geology: 60 million years ago an enormous lava flow covered the Antrim plateau, up to 90 metres deep in places. As it cooled slowly from the top and bottom simultaneously, it contracted and cracked in regular fracture lines. Where cooling was perfectly even, the cracks are hexagonal — the most efficient way to divide a plane into regular polygons, the same mathematics that appears in honeycomb. Most columns are 5 or 6-sided; some have 4 or 8. The tallest rise to 12 metres. At the main causeway area you can walk on and between the columns at sea level, their tops forming an irregular stepping-stone platform extending from the cliff base into the sea.

The visitor centre sits on the clifftop, a 10–15 minute walk above the columns. Minibuses run down; walk instead. The descent gives you the first view of the formations as you come around the headland, which is worth arriving on foot for. On the causeway, the most photogenic formations include the Giant's Boot (a column shaped like a shoe, near the main causeway area), the Organ (tall columns on the eastern cliff face curved like organ pipes) and the Chimney Stacks (isolated sea stacks east of the main area). Continue east past the main causeway toward the Amphitheatre for the Chimney Stacks — fewer people, equal geology.

The causeway itself is free. You pay for car parking at the visitor centre (around £13) and the audio guide (optional). If you're arriving by bus, there's no parking fee and you can walk past the visitor centre and down to the causeway without paying anything.

Getting here without a car: Translink's Antrim Coaster bus (252) runs along the north coast from Belfast to Portrush and passes near the causeway — allow about 2.5 hours from Belfast. Alternatively, take the train from Belfast to Coleraine (55 minutes, about £10), then the Causeway Rambler bus (172) which runs in summer between Coleraine and Ballycastle via the Giant's Causeway. The Translink Day Tripper ticket covers unlimited bus travel across Northern Ireland for around £10 — worth buying if you're spending a full day on the north coast.

The Causeway Coastal Route — the A2 from Ballycastle to Portrush — covers Carrick-a-Rede rope bridge (18 km east), White Park Bay beach, Ballintoy Harbour, Dunluce Castle (3 km west) and Bushmills village (3 km west, home to the world's oldest licensed whiskey distillery, established 1608) in 30 km. Doing all of these in a day requires an early start from either Ballycastle or Portrush. Both have hostel accommodation; Portrush is a proper seaside town with cheap food and good craic in summer.

Note: Northern Ireland uses GBP, not euros, and prices are generally lower than the Republic. This is one of the more affordable days in Ireland.