The Hudnalls is one of three national nature reserves in Gloucestershire that protect sections of the extensive, partly ancient woodland of the Wye Valley, along the England-Wales border; Highbury Wood and Lady Park Wood are the others. Named after the nearby settlement of Hudnalls, just west of St Briavels, the woodland extends for nearly a mile along the steep east side of the valley, spanning over 400 feet of elevation and containing large areas of beech, plus ash, silver birch, elm, lime and oak, both sessile and pedunculate. The reserve is part of the larger Hudnalls Site of Special Scientific Interest, which includes a smilarly-sized block of woodland to the north, aligned east-west.
The woods are classed as semi-natural, having been coppiced, pollarded and otherwise managed in the past, though not for a century or more. The tree composition can vary over a short distance, due to differing soil types - a consequence of the bedrock, which ranges from alkaline limestone to (mostly) acidic Old Red Sandstone. The reserve is notable for several rare tree species including large-leaved lime and a few types of whitebeam, while other points of interest are a good range of fungi and bryophytes, plus wildflowers, both in the wood and in the unimproved grassland around the perimeter, and the moister terrain bordering the river.
While some parts of the wood are long-established, others have developed over the last two or three centuries, having previously been rough pasture. The land in the central part of the NNR is crossed by an old track lined by the remains of several stone dwellings and field boundaries, from a settlement established here around 1750, inhabited for only around a hundred years, since which time the pasture has transitioned to woodland.
The nature reserve is not directly accessed by any roads, only by paths, one along the lower edge, beside the River Wye, others that approach from the higher ground to the east, starting from narrow country lanes. Parking is very limited hereabouts; only on the occasional verge or beside field entrances. Two main approaches are from the north, a track near Hudnalls Farm, and a short distance south along another track to 'Fayland', a house in the woods - a private driveway, but accessible to pedestrians. From here a path continues downhill a way, past a photogenic ruin ('Cop Well'), and into the NNR, then traverses southwest emerging to the open, flat land aside the river near the south edge of the reserve. Ground cover in the woods is generally light and it is possible to walk cross-country across most areas of the woodland. A few minor streams flow down the valley sides, some associated with alder. The wood can also be entered from the south side, at the end of a road from Brockweir.