The map’s contour lines, tight and strained, warned of steep slopes careering down towards the Afon Tywi. Otherwise, it showed little of what to expect from the Gwenffrwd-Dinas RSPB reserve. This 600 hectares of Atlantic oak woodland, glorious though it is, is a mere remnant of what once was a much larger Celtic temperate rainforest, covering most of the west coast of Britain. This kind of habitat is increasingly rare, and indeed it feels aptly precious. Water is monarch here, sustained by westerly Atlantic storms. Rains decant through tree canopies, and creep into cracks and crevices in gnarled sessile oak boughs, while moss cushions trap and retain the water, maintaining forest humidity. Epiphytic ferns cling to oak branches like arboreal hitch-hikers. Mosses not only pave the forest floor, but also creep up fence posts and drape over fallen stones. We followed a boardwalk into the woodland. Green was resurgent, the palette of spring, a mosaic of emerald, olive and sage. Tissue-paper thin leaves, emerging under spring warmth, imposed a gentle, verdant light. If the boardwalk wasn’t a clue enough to marshy ground below, a leafy profusion of hemlock water-dropwort, a few alder and glimpses of dark peaty soil confirmed that water lingers here. The boardwalk merged into a footpath. Among increasing cover of willow, downy birch and oak, we caught sight of a monochrome flicker: a male pied flycatcher, with a female perched close by. A male common redstart, its tail flashing like fire, landed further along a fence. A distant cuckoo called, my first of the year. Our joy was complete when we spotted and heard the unmistakable coin-spinning song of a wood warbler. A splinter of sound alerted us to a goldcrest. Having lost my high-frequency hearing, I can only hear goldcrests when they are close, so I was delighted to catch what the writer Tim Dee calls their “fuse-wire call”. This tiny forest sprite, flitting among branches of oak, flew down to a cluster of side shoots and disappeared. Focusing our binoculars, we realised it had a nest: a fragile hammock quilted from spider’s web, moss stems and lichen fragments melded among the branches. As we gazed, a burst of golden feather and an eye stared back at us. Bluebells spangled the woodland floor, flowering later than in my north-west home. Huge ancient rocks had tumbled downslope to the Tywi, one providing a dipper’s diving board. Trees thinned, slopes eased and light flared as our walk came to an end. A friend whispered: “This place is magical”. It is.