Find the Watergate, the twin-turreted tower Cole added to the river front in 1609

Go through the Fermanagh County Museum inside the castle

See the Inniskillings regimental collections

Work out why an island where the Erne narrows was worth a castle from 1428 onwards

Hugh Maguire built a castle at Enniskillen in 1428 on the island where the Erne narrows, controlling the only crossing between the upper and lower lough — which is why the town is there at all. The Coles remodelled it after the Plantation and added the Watergate, the twin-turreted riverside tower, in 1609. It was besieged unsuccessfully by Rory Maguire in the 1641 rebellion while sheltering Protestant settlers, and it now holds the Fermanagh County Museum and the regimental museums of the Inniskillings.

Enniskillen Castle: The Maguire Watergate

Tour the house and look at how exactly Wyatt's neoclassical proportions are held

Look at the Portland stone façades and the Ionic portico, and think about shipping that stone from Dorset in the 1790s

Walk the 1,200-acre wooded estate and the lough shore

See the state bedroom prepared for a royal visit that never happened

Armar Lowry-Corry, 1st Earl Belmore, built Castle Coole between 1789 and 1798 as a summer retreat, and spared nothing doing it: James Wyatt designed it, the façades are faced in Portland stone brought from Dorset, and the portico carries sober Ionic capitals. It is about as pure a piece of neoclassical architecture as exists in Ireland, standing in 1,200 acres of wooded estate that the family had held since the Belfast merchant John Corry bought it in 1656.

Castle Coole: Wyatt's Portland Stone Palace

Take the boat out to Devenish from Enniskillen or Trory Point

Find the four windows at the top of the round tower, one for each point of the compass

Find St Molaise's House and Teampull Mór below the tower

Climb to St Mary's Priory on the hilltop and find the carved high cross in its graveyard

Find out what happened here in 837 and in 1157

Devenish Island in Lower Lough Erne was the site of a monastery founded by St Molaise in the 6th century. It was raided by Vikings in 837 and burned in 1157, and it carried on as a parish church and, from the middle of the 15th century, as St Mary's Augustinian Priory. What stands now spans all of that: St Molaise's House, a small 12th-century church; a 12th-century round tower, 81 feet high, with four small windows at the top facing the four points of the compass; Teampull Mór, the lower church; and on the hilltop the priory's church, tower and small cloister, with a carved 15th-century high cross in the graveyard. Boats go out from Enniskillen and Trory Point in the visitor season.

Devenish Island: St Molaise's Monastery on Lough Erne

Walk out to the Irish Yew, about a mile south-east of the house in the old 18th-century gardens, and stand under the parent of almost every one in the world

Work out why a tree that cannot set viable seed is now on every continent

Tour the 18th-century house built by the Cole family, Earls of Enniskillen

Walk the estate towards Cuilcagh, where the two saplings were found in 1767

In 1767 a farmer called George Willis found two odd yew saplings on Cuilcagh mountain — upright, columnar, nothing like a normal yew. One died. The other was planted at Florence Court and is still alive. Because the Irish Yew cannot be grown from seed and propagates only from cuttings, almost every Irish Yew in every graveyard and garden in the world is a cutting from a cutting from that one tree. The house it stands behind was built by the Cole family and named for Florence Bourchier Wrey, who died in 1718.

Florence Court: The Mother of Every Irish Yew

Take the underground boat journey along the Cladagh River when water levels allow it — the tour runs about 75 minutes either way

Walk the show cave passages beside the Owenbrean River, in a system first explored in 1895

Note the cave's full surveyed length — 11.5km, the longest known in Northern Ireland, of which the tour covers a small part

Book ahead — Marble Arch Caves tours are timed and can sell out in peak season

Marble Arch was first explored in 1895 by Édouard-Alfred Martel and the Dublin naturalist Lyster Jameson, and when the underground water levels allow, the tour still starts the way the cave does — by boat along the underground Cladagh River. Otherwise you walk the passages beside the Owenbrean under the Fermanagh hills. The whole trip takes about 75 minutes and covers a small part of the 11.5km surveyed so far, the longest known cave system in Northern Ireland. Tours are timed and sell out in season, so book before you drive out.

Marble Arch Caves: The Cladagh River Boat Journey

Walk the Calf House Dolmen Trail from the interpretative centre

Find the Giant's Leap wedge tomb, one of the most intact in Ireland

Find the erratic boulders the ice left on the plateau

Look for the boulders carved with prehistoric rock art

Cavan Burren Park sits on a limestone plateau about 295 metres up under Cuilcagh Mountain, in the Cuilcagh Lakelands Geopark, and it is one of the finest prehistoric landscapes in Ireland. It holds wedge and portal tombs going back to the Neolithic — among them the Calf House Dolmen, the Tullygobbin wedge tomb and the Giant's Leap wedge tomb, one of the most intact wedge tombs on the island — with cist graves, relict field walls, hut sites, a promontory fort and boulders carved with prehistoric rock art. The ice left huge erratic boulders scattered across the plateau, and the Giant's Leap is the bed of a vanished river. Five trails run from the interpretative centre; entry is free and it is open all year.

Cavan Burren: Tombs and Erratics on the Limestone

Walk the boardwalk out across the blanket bog to the foot of the mountain

Climb the stepped section to the viewing platform at the top of the boardwalk

Look out over the Fermanagh lakeland and into Cavan from the platform

Find out why the boardwalk was built in the first place — to stop walkers destroying the bog

The Cuilcagh Boardwalk Trail was built in 2015 for an unglamorous reason: walkers were destroying the blanket bog underfoot, so a raised timber walkway was laid across it to protect the peat. Then it went viral, got nicknamed the Stairway to Heaven, and started drawing far more people than anyone planned for. The walk itself is genuinely good — a long approach across open bog, then a steep flight of steps onto the cliff-edged summit plateau of hard Lackagh Sandstone, with the Fermanagh lakeland spread out below.

Cuilcagh: The Stairway to Heaven Over the Blanket Bog

Walk the harbour and the lock where the canal drops into the Shannon

Find the ruins of the canal hotel that housed passengers overnight

Walk the Grand Canal towpath east from the harbour across the bog

Have a pint in one of the two pubs and watch the boats work the lock

Shannon Harbour is where the Grand Canal finally reaches the Shannon after crossing the bogs from Dublin, and for a century it was one of the busiest inland ports in Ireland — passengers and freight transferring between canal boats and river steamers, with a hotel to hold them overnight. The traffic went and the village stayed: a handful of houses, a lock, docking for boats, and two pubs. It is one of the quietest places on the whole waterway, and the junction survives largely as it was build canal junction in the country.

Shannon Harbour: Where the Grand Canal Meets the River

Walk the full length of the Mall, the Georgian green the city is built around

Go into the Robinson Library, founded in 1771 when the archbishop opened his own collection to the public

Find the copy of Gulliver's Travels carrying Swift's own handwritten notes

Walk from the library to the observatory Robinson also founded, on the hill above

Archbishop Richard Robinson set out to make Armagh a city worthy of being the ecclesiastical capital of Ireland, and much of what he paid for is still standing — the observatory, the public buildings, and the Mall, the long Georgian green the city is arranged around. In 1771 he founded a library by the simple method of opening his own collection to the public. It is still there, and on display in it is a copy of Gulliver's Travels carrying handwritten notes by Swift himself.