The most important habitat of this diverse site is the rare wet woodland bog areas. A number of small streams flowing through the site spread out to form boggy areas known as mires, undermining tree roots and causing them to crack or the trees to fall prematurely. Fallen wood combined with the underlying peat soils, leaves and sphagnum moss rots away to form more peat bog.

There are 65 species of moss and liverwort here, which include sphagnum and star mosses, with tufts of rush and other wetland plants and fungi. This provides ideal conditions for the larvae of many invertebrates, which provides food for many charismatic birds including curlew, cuckoo, woodpeckers and finches that rely on the nature reserve for food or shelter.

Following the main footpath to the moorland commons above gives a stunning view onto the mires and across the whole nature reserve down the valley.

• Spring: Plants - Wood sorrel; Marsh violet; Birds - Curlew; Cuckoo; Blackcap
• Summer: Plants - Marsh orchid; Cotton grass; Heather; Harebell; Bird's-foot trefoil
• Autumn: Fungi; Birds - Jay; Redwing; Fieldfare
• Winter: Birds - Woodcock; Red grouse; Tawny owl; Long-tailed tit; Mammals - Brown hare

The area was home to the Cragg Vale Coiners, an infamous gang of local criminals who produced fake gold coins in the late eighteenth century.

If you like social history arrange to also visit nearby Coiners Barn.

Public transport
Mytholmroyd has a station and regular buses from Halifax and Burnley. National Cycle Route 66 crosses the B6138: for cyclists who like a challenge this road is the longest continuous climb in England.

By car
Take the B6138, signposted Littleborough until ½ mile from Mytholmroyd, the houses on the right give way to fields. Visitors’ vehicles are not allowed to use the track to the nature reserve and should be parked on the roadside. Immediately before the road swings left and right to cross Dauber Bridge, there is a track on the right, with a public footpath sign to Frost Hole. Walk along the track for about a ¼ mile, fork left onto the concrete road until you reach the main entrance (0.6 miles from the road).