The Brecon Beacons National Park is the kind of place where scale does things to you, wide moorland, deep river gorges, waterfalls dropping through ancient woodland and skies that go dark enough at night to justify the park's International Dark Sky Reserve status. It's one of Britain's great landscapes and it barely requires anything beyond a pair of decent boots.
Walking, wild swimming in the Usk or Taff, cycling the canal towpath, or doing nothing except existing in a landscape this expansive, all equally valid uses of the park.