Is she your dog, we ask two men on a boat as a large black lump of love leans on our legs and we stroke her glossy coat. “She might be yours now,” one of them answers. She’ll adopt any dog-loving passerby on the towpath of the Barrow. She fell into the river as a pup, and now she’s wary of the boat, they explain.

A short way back down the river I conquer my own wariness, and hang between a slippery rock and a hard steel ladder before giving in to the silty coolness of the pool above the weir at Clashaganny for my first river swim in decades.

Olivia O’Leary wrote a piece more than a decade ago about being joined by an otter while swimming here with her sister. It was a memorable love letter to the beauty of a river and its surrounding countryside.

Today in dappled sunlight it is as magical as she described. After a few minutes walking out of Graiguenamanagh we have left the sounds of people and traffic for birds, wind and the river. Frothy Queen Anne’s lace bobs in the breeze along the edges of the grassy path. Something leaps in the water. Swallows skim the surface for flies.

Waterways Ireland wanted to upgrade the 115km walking route from Lowtown, in Co Kildare, to St Mullins, in Co Carlow, to a greenway or, the Barrow Blueway as they called it. Objectors said this would ruin it. In April the plan was rejected by An Bord Pleanála. A middle ground between conservation and an improved path seems possible. But, for the moment, the Barrow Way is a hidden treasure.

A year and a half ago the chef Stephen McArdle left the buzz of Dublin’s restaurant strip on St Andrew’s Street, where he ran Stanley’s wine bar, for a quieter flow of life in the Co Kilkenny town of Graiguenamanagh.

We have booked a late lunch in Barrow’s Keep, the restaurant McArdle runs with one of the country’s best sommeliers, Morgan Vanderkamer. Having walked away from Graiguenamanagh, we need to decide when to turn back to make it in time. The urge to “just go to the next bend” has left us running late, but we phone to let them know we’re still coming.

We feel the kilometres walked when we sink gratefully and hungrily into caramel-coloured leather chairs in this lovely room, with its teal-painted panelling, white tablecloths and small windows set into thick old walls. We are properly hungry, and there are fewer more perfect spots for us to end up.

This is confirmed with the freshly baked stout-and-treacle bread, served with room-warm butter. Sunday lunch here is €28 for two courses. You could easily pay more for a soul-sapping carvery in a greasy pub. Instead there’s a plate of house-cured salmon with ribbons of pickled cucumber and summery dill that’s everything I could want.

A “salad of carrot, red onion, Cashel Blue and walnut” could be dull as ditchwater in some hands, but here it’s spears of bright purple radicchio for scooping the perfect cheese and candied walnuts, along with ribbons of pickled carrot, light and lovely. Crab from Kilmore Quay is the star of the third starter, with summery beets, pickled and petalled or roasted and cubed to show off their candy pinkness with the gorgeous seafood.

Ashe’s roast striploin of beef is the biggest, Sundayest plate of dinner, a lusciously juicy slice of meat with mash and roasties and sweet roasted carrots, and a slather of the loveliest horseradish sauce on the meat to slice through it like a spear.

I have scallops, also landed at Kilmore Quay, with butter-fried cod resting on that great mash and a soup of asparagus and broad beans and charred fennel to bring all the summer. Amy gets the black sole, a beautifully cooked specimen as well cooked as you would find, for considerably more euro, in any Paris bistro. It gets us talking about the impossibility of life with someone who didn’t like food.

Meringues made with eggs from Tinnock Farm and fat, juicy Irish strawberries with a lemon cream make for the perfect summer dessert. Then there’s chocolate several ways, a rectangle of spoon-sticking ganache, a brownie with caramel and an espresso ice cream that’s some of the best house ice cream I’ve tasted. We finish with that need for a postlunch lie down. (Could they install a nap room upstairs?) We head home with the feeling that we may have just had the perfect summer Sunday.

Barrow’s Keep is a jewel in this slightly forgotten place. Although it’s the bank-holiday weekend, the crowds are elsewhere – in Kilkenny for the comedy or at Gowran for the races. This summer, book a table and set off down the towpath with your togs and a towel. Graiguenamanagh may not have a blueway, but it has Barrow’s Keep, and that is a huge reason to visit this gorgeous place.

 Lunch for three with soft drinks and sparkling water and two shared desserts and cheese came to €114.25

• Verdict A beautiful restaurant in a beautiful place
• Facilities Nice
• Wheelchair access Yes
• Vegetarian options Limited but good
• Food provenance Good. Tinnock Farm eggs and Kilmore Quay crab
• Music Lovely jazz