Go Walk: Barrow Valley, Co Carlow

One late August day I was swimming with my sister above the weir at Clashganny. The sun glanced off the water. Under the bank, fat blackberries dipped down into the river. Suddenly beside us was the wet dark head of an otter. He paddled along quietly. So did we. River etiquette, as Mole and Rat would tell you, forbids any sort of comment on the sudden appearance or disappearance of one's friends.

This is summer for me: long lazy hours by the river; friends strolling down the towpath as day wears on. We swim over to the weirs and lie back on the mossy stones, letting white water bubble over us. All around is the dizzying roar of the water, the silty smell of its churn. The bank faces west or southwest, so on good days it stays warm until sunset, when the river turns gold and the fish are jumping and there's an echo all down the valley.

Even when it's raining, which it was most of last summer, you can still lose yourself down here. It's quiet. People have all the courtesy and reserve of an area that has never had to rely on tourism. They'll leave you alone. You won't meet half of Dublin. There's no sparkling sea. There are no public gulls. This is intimate, the heart of the country.

The Barrow Valley is where I'm from, south Co Carlow. The river defines the county on the west, Mount Leinster and the Blackstairs define it on the east. In between, you can go swimming, canoeing, boating, cycling, climbing, riding, golfing, but, most of all, this is country made for walking.

I'll describe the most beautiful walk, also the simplest. It runs all along the grassy towpath of the Barrow and Grand Canal waterway and brings you through some of the most beautiful riverscape in these islands.

It starts at Ballytiglea Bridge, above Borris, and ends in St Mullin's, at the southern tip of the county, a walk of about 18km but one that can be easily divided into three sections of about an hour point-to-point, or two hours if you double back. The way is flat. Waterways Ireland keeps the grass mowed, so it's very easy to walk. And all the way, except when the river cuts through Graignamanagh, you'll be away from roads and cars and noise. It will be as though a door has shut behind you and you'll be tempted never to open it again.

Heading south from Ballytiglea, you'll have Borris House demesne for a kilometre or two on your left. You'll pass Borris Lock and come to Bunnahowen - we learned to swim there, in the freezing Mountain River, and then, as we got stronger, floated out under the old stone bridge into the deep and warmer Barrow. It was our down-home version of a plunge pool and hot tub.

The next lock you come to is Ballinagrane, its long weir, like all weirs, guarded by a hungry heron. It'll push off resentfully as you approach, but it'll be back as soon as you round the corner. On then to Clashganny, one of the few places where a car is allowed near the line, so someone can pick you up if you're tired.

Bring your togs, because Clashganny (or Sandy Valley) is a perfect place to swim. Above the lock and opposite the weir there's a full-time lifeguard in July and August. Here, there are steps down to the water and, on the weir side, a breakwater to dive off.

The next leg of the walk is from Clash to Graignamanagh. There are deep woods above you all along the left. The river splits off for Clohastia on the right - you can hear the weir.

You'll head along the quiet canal bank to Ballykeenan, the only double lock on the river and the deepest. There the river rejoins you - you'll see the ancient eel weir on the other side of the island and you'll bowl along the stretch to Graignamanagh.

Take a bit of time in Graig. Cross over the graceful Palladian bridge built by a pupil of George Semple in the 18th century and walk up to the 13th- century Duiske Abbey. The biggest Cistercian foundation in Ireland, it was restored in the 1970s to its original soaring roof height. The old floor tiles with their fleur-de-lis pattern can still be seen, as can the magnificent Romanesque processional doorway.

Before you resume your walk, I might as well warn you. Last time I checked, there was nowhere to eat in St Mullin's and nowhere to drink if Blanchfield's pub is closed, so grab something in Graig. You can have a great coffee and sandwich at Coffee on High, on High Street, a good carvery lunch in the Duiske Inn, on Main Street; two good Chinese restaurants, one on Main Street and one in Tinnahinch.

New on the Tinnahinch side of the bridge is Boats, a bistro with an Italian chef, open from the end of March. It will serve food from 11am with a lunch-type menu until 7pm and after that a more sophisticated dinner menu.

Graig is an old canal port, and the boats and the ducks gather on either side of the bridge. You'll be tempted to stay, but press on down the towpath past Upper Tinnahinch Lock and you come into one of the loveliest stretches of the river. You'll pass the ruined Butler Castle at Tinnahinch and walk on down to where the woods rise high on either side and the town and the traffic die away.

The river is wide here, and the woods are deep and full of life. I've watched a stoat on the towpath rise to its hind legs and sniff the air as I waited in the shadow of the trees. Walking along here in the dusk, I've seen grey owls swoop low over my head. There's a rustling in the undergrowth all the time as you walk along, and you wonder how many wild things are watching.

Three locks on, you'll reach the end of the canal way at St Mullin's, with its Dutch-looking lock house and its little harbour of boats. Now you'll be conscious of mudflats, of the river changing. Though the sea is 50km away, from here down the river is tidal. If you're lucky as you arrive around the bend, the tide will be in, the water brimming and all the deep dark beauty of St Mullin's on show. Your walk is ending not just with a pretty village but with a wealth of history.

Here, towering above the river, you'll find a Norman-period motte and bailey built in even earlier pre-Christian remains. In the graveyard, you'll find the base of a round tower and the remains of four churches said to have made up the monastery of the seventh-century local saint, St Moling, the man who is said to have got rid of the infamous borumha, or cattle tax. (The Book of Moling, which details his exploits, is displayed in the same case as the Book of Kells at Trinity College Library).

Moling's Holy Well is nearby, and locals visit it on his pattern day, in July, and also visit the graves here of many of the 1798 dead. Traditionally, this graveyard is said to be the burial place of the kings of Leinster, including Art McMurrough Kavanagh - a gravestone marks the spot.

This is Kavanagh country, and you have a chance to hang out at the McMurrough Kavanagh seat, Borris House, this July when it hosts Blackstairs' Opera in the Gardens (all details when finalised on www.blackstairsopera.com). You can picnic beforehand in the gardens and see the whole of the Blackstairs range and Mount Leinster laid out before you. It's magic. So is the opera.