Here is a selection of those easiest to get to:
Llangors Lake which boasts a birdhide on its western shores and where wildflower meadows are alive with butterflies in summer. Or else try the National Nature Reserves at Craig y Cilau, Craig Cerrig-gleisiad, or try Ogof Ffynnon Ddu near Pen-y-cae in the Upper Swansea Valley where you can see one of the best areas of limestone pavement in the Park.
Talybont Reservoir is good for wintering and migrant birds and you can marvel at the sheer diversity of mosses, liverworts and fungi in the wonderfully rich woods of the Waterfalls area.
Talgarth is an excellent centre with Llangors nearby and superb woods where you can see bluebells, wood anemones and wild garlic in the Spring like the Brecknock Wildlife Trust's Pwll yr Wrach reserve or Woodland Trust's Park Wood close by.
Lastly there are spectacular beechwoods at Cwm Clydach gorge and rich oak and hazel coppice at Cwm Coed y Cerrig.
Wherever you go, remember to avoid disturbing any wildlife and its home and to follow the Countryside Code.