Cladagh Glen is a National Nature Reserve protecting long-established ash woodland and its natural inhabitants, including feral goats, red squirrels and pine martens. Some of the layered bedding planes of limestone are over 300 million years old. From the car park at the old stone Cladagh Bridge, follow the sign-posted route upstream along the river. About 500m up the path on your left are the Cascades, where water emerges from an underground cave and pours in sensational fashion over a natural rock ‘staircase’. This water has had an underground journey from a swallow hole called the ‘Rattling Hole’ further up the hillside. The trail continues up the narrow, steeply sided gorge past numerous small rapids until you reach Marble Arch itself, an arch of limestone that the river has sculpted as it emerges from the caves below. Take a tour of the caves before returning back down the glen; a perfect way to experience the ecology of this ‘karst’ landscape from both above and below the ground.