Llyn Du

Dark waters reflect the surrounding hills at this remote mountain lake, whose Welsh name literally means 'black lake' - and you'll see why when you peer into its deep, peat-stained depths. The walk up takes about 45 minutes from the nearest parking spot, following sheep tracks through rough moorland that gets properly boggy after rain. Worth bringing waterproof boots.

Families with younger children might find the trek a bit much, but older kids who don't mind a proper walk will love the wild swimming opportunities in summer. The water's cold even in July, mind you. Serious walkers often use Llyn Du as a waypoint for longer routes across the surrounding peaks.

There's no facilities whatsoever - this is proper wilderness territory near Bwlch-y-ffridd. Pack everything you need and take your rubbish home. The lake makes a cracking day out from any of the holiday parks scattered around this part of Powys, with Sunny View Caravan Park and Carmel Caravan Park both within easy driving distance.

Best visited on clear days when the mountain reflections are sharp as glass. Early morning or late afternoon light transforms the place completely. If you're staying at somewhere like Maesmawr Farm Resort, it's well worth the detour for a taste of Mid Wales at its most untamed.