Like many nature reserves, Coed-y-Bedw contains a patch of ancient, broad-leaved woodland, prettiest in springtime when the ground is carpeted with dense fields of bluebells and wild garlic, but here the scenery is enhanced by several streams running through, and the plant and animal life is made more varied since the wood spans the boundary between acidic and basic bedrock.
The trees cover steeply sloping land on the north side of a hill near Pentyrch, five miles northwest of Cardiff, with the main stream (Nant Cwm-llwydrew) flowing through a shallow valley at the base, and two tributaries trickling down from the upper reaches, fed by springs, one of which has a name, Ffynnon Gruffydd. Waters from these two are calcareous since the higher elevations are underlain by limestone rock, while the lower slopes have acidic soils, including coal measures and seams of iron ore (haematite), which were mined on a small scale in the 19th century - relics include excavations, tramways, spoil heaps and the arch from a tunnel entrance, all overgrown and barely recognisable, and a ruined stone cottage once occupied by the mine owner, and poet, Morgan Thomas. The mining ceased in 1913.
The varied soils result in different plants, such as lousewort, heath bedstraw and bluebells in the lower, moister, acidic areas, with garlic and spindle on the upper, calcareous band. Animals of note are mostly birds and invertebrates.
A relatively busy road, Heol Goch between Pentyrch and Morganstown, runs along the south edge of the nature reserve, and from here several paths descend towards the valley floor, linking with two transverse routes, allowing a loop walk of up to one mile.
Coed-y-Bedw Nature Reserve, which is not obviously signposted, extends for nearly half a mile along the north side of Heol Goch. The only suitable parking place is at the wide entrance to a private road to the south, leading to the Ton Mawr Quarry. One path into the reserve starts opposite, next to an inconspicuous notice, entering mixed ash woodland with relatively light undergrowth; lower down, other trees include oak, birch and beech. This path very soon connects with a generally wider track below, closer to the stream. This does not usually carry much water but there is sufficient to create many pretty pools and small cascades, and it is followed by the path about half of its length, as in other places the creek flows between steeper slopes, where the trail has to move above. Also along the lower path is one of the few more open areas, centred on a pond lined with reeds, iris and wild garlic. The ruined cottage is also close to the stream, towards the west side of the reserve; once a two story building with attached stables, it now consists just of low, broken, moss-covered walls.