Get out on Lough Oughter by boat or kayak to reach the castle island

Walk right round the circular keep on its island

Find out how a castle came to be built on what may be a man-made island

Walk the trails at Killykeen Forest Park on the lough shore

Cloughoughter is a circular stone castle standing on a tiny island in Lough Oughter, four kilometres east of Killeshandra, and the only way to it is by water. The island may be a crannog — an artificial one — with fortification here possibly as early as the 6th century. The O'Reilly chiefs of East Breifne held it for centuries, and Owen Roe O'Neill, commander of the Ulster Army, is said to have died there in 1649. It sits out in the water with no road, no path and no signage, which is exactly why it looks the way it does.

Cloughoughter: A Round Castle on a Cavan Island

Paddle out into the Lough Oughter channels from Killykeen

Walk the forest trails and the lakeshore loops through the park

Work out how a drumlin field turns into a lake with no shape to it

Paddle within sight of Cloughoughter Castle out on its island

Lough Oughter is not really a lake but a flooded drumlin field — water filling every hollow between hundreds of small round hills, so what looks like a lake on the map is a maze of channels, bays and wooded islands with no obvious way through. Killykeen Forest Park sits in the middle of it with 240 hectares of woodland, and the best way to understand the place is from a canoe, working out the route as you go.

Killykeen: Paddling the Lough Oughter Maze

Paddle a multi-hour canoe or kayak route through the interconnected lakes of the Lough Oughter complex

Reach Drumlane Abbey near Milltown and find the round tower beside the ruined Augustinian church, on a site that goes back to St Columba and St Mogue

Photograph the round tower's doorway, set several metres above ground level — built high to hold the near-foundationless tower together rather than to keep raiders out

Walk the ruined nave of Drumlane's medieval church beside the tower and find the graveyard's oldest legible headstones

Christianity is said to have come to Drumlane around 555 with St Columba, and St Máedóc — St Mogue locally — founded the early monastery; what stands by the water now is a ruined Augustinian church and a round tower. It stands on the edge of the Lough Oughter lake complex, one of Ireland's largest connected inland waterway systems.

Drumlane Abbey and the Cavan Waterways

Drive the lake roads north-west of the town and count how many loughs you pass

Walk in Killykeen Forest Park among the drumlins and the water

Find out why the ice left Cavan with this many small hills and this much water

Fish or paddle on one of the loughs — most of them have no one on them

Cavan is the county of the drumlins and the lakes, and the local boast is that there is one lake for every day of the year. The truth is close enough: the ice left a field of small rounded hills, the water filled every hollow between them, and the result is a landscape where the road bends constantly because it has no choice. Lough Oughter is really one continuous flooded maze rather than a lake, and the town sits in the middle of it all.

Cavan Town and the Lakeland Drumlins

Take a boat out on the Erne from the town harbour

Walk Butler Street down to the Diamond and round the town's buildings

Work out why the isthmus made this the crossing point

Follow the Shannon–Erne Waterway south and see how far it would take you

Béal Tairbirt means the mouth of the isthmus — the narrow neck of land between the Erne system and the drumlin lakes, which is why a town grew here and why it is now one of the main boating harbours on the Shannon–Erne. The main street runs down to the Diamond with the town's buildings around it, and below that the river. Since the Shannon–Erne Waterway reopened in 1994 you can take a boat from here the whole way to Limerick.

Belturbet: The Mouth of the Isthmus on the Erne

Walk the woodland trails down to the shore of Upper Lough Erne

Walk the old parkland trees of the demesne above the shore

Take a boat out among the islands and reedbeds of the upper lough

Look at riparian woodland growing straight into the water and work out why so little of it is left

Crom is 1,350 acres of nature reserve along the shores of Upper Lough Erne, mostly riparian forest — woodland growing right down into the water, which is a habitat that has almost vanished from Ireland. The National Trust runs it as one of three Fermanagh estates alongside Florence Court and Castle Coole. It is quiet in a way that few places are: islands, reedbed, old parkland trees, and water on every side.

Crom: Riparian Forest on Upper Lough Erne

Walk into the two roofless medieval churches at Fenagh

Find the megalithic tombs in the fields around the abbey, older than the monastery by millennia

Find out what the Book of Fenagh is and what it records about Caillín

Stand where a divinity school drew students from across Europe to a Leitrim field

The Book of Fenagh has Caillín coming here from Dunmore in Galway in the 5th century, though historians put him a century later, according to the Book of Fenagh, and founded one of the oldest monastic sites in Ireland — from the very earliest period of Celtic monasticism. Its divinity school was celebrated enough that students came to this Leitrim townland from every part of Europe. Two roofless medieval churches stand there now in a field, with megalithic tombs in the ground around them that are far older again.

Fenagh: The Divinity School Students Came to From All Over Europe

Climb Millmount and go into the Martello tower shelled in the Civil War in 1922

Go through the Millmount Museum below the fort

Find the preserved head of St Oliver Plunkett in St Peter's Church

Walk the Boyne quays and find where Cromwell breached the walls from the south in September 1649

Stand under St Laurence's Gate — the twin-towered barbican that guarded the east gate, which has itself vanished

Drogheda, the largest town in the Republic, has more history packed into it than most Irish cities and gets a fraction of the visitors. Millmount stands on a great mound on the south bank of the Boyne and has been the town's strong point since the Normans — through Cromwell's assault in 1649 and on to 1922, when its Martello tower was shelled almost to pieces in the Civil War. Across the river in St Peter's, the preserved head of Oliver Plunkett has lain since 29 June 1921: Archbishop of Armagh, hanged at Tyburn in 1681 as the last victim of the Popish Plot, beatified in 1920 and canonised in 1975, the first new Irish saint in almost seven hundred years.