Sillent Valley Reservoir

The water here is so clear you can see straight down to the rocky bed, even when you're standing on the dam. Silent Valley Reservoir is a proper working water supply for the area, but the walking trails around it feel more like you've stumbled into somewhere remote and untouched. It's set deep in the Mourne Mountains south of Newry, with the peaks rising sharp all around you.

You can walk the full circuit - takes about an hour at an easy pace - or just potter along the shoreline if you're not in the mood for anything strenuous. The water reflects the hills back perfectly on calm days, which is when you should go if you want photos. Windy afternoons are less forgiving, but they clear the crowds out fast. It's free to visit and the car park rarely gets rammed even in summer.

Walkers will love this more than families with young kids - there's no shops, no facilities, just you and the water and the wind. Bring proper boots because the terrain's uneven in places. It's worth combining with other Mourne walks if you're staying at one of the nearby glamping spots like Oakwood or Willowtree, or the camping options scattered round Annalong way. You could easily spend a morning here then head into the villages for lunch. Don't expect signposted tourist infrastructure - this is the kind of place people come to precisely because it's not fussed about visitors.