St. Teilo's Pool

Water so clear you can see the bottom twenty feet down - that's St. Teilo's Pool, a glacial lake tucked into the hills above Builth Wells in Powys. It's small, maybe a couple of hundred metres across, but the depth is proper impressive for Mid Wales. The water has that eerie blue-green quality you get in mountain pools, and on a still day it's genuinely striking.

Getting here means a decent walk through farmland and forest - nothing brutal, but it's not a five-minute stroll from the car park either. You'll work for the view, which somehow makes it feel more worthwhile. The pool itself sits in a steep-sided bowl, so there's no sprawling beach experience. This isn't a swimming spot (and the water's cold enough year-round that you wouldn't want to linger). It's purely visual - walk in, take it in, walk out.

History types will get a kick from the name: St. Teilo was an early Welsh saint, and the pool carries weight in local folklore. Walkers use it as a waypoint rather than a destination, which is probably the right way to approach it. Families with very young kids might find the walk frustrating for the modest payoff, but teenagers and keen hikers will appreciate the effort.

Great House Farm is practically on your doorstep at less than a mile away if you're staying in the area. Time it for early morning or late afternoon when the light hits properly - midday can wash out the colour. Allow an hour including the walk.