THIS is an undulating walk with a number of gates and stiles. The route explores the stunning area around Malham using open access land owned by the National Trust. Part of the route follows rough fields with slippy limestone outcrops.

NESTLING at an altitude of 375 metres is Britain's highest upland alkaline lake, Malham Tarn, which forms a key part of the Malham Tarn National Nature Reserve.

And the tarn - reputedly the setting of Charles Kingsley's classic children's novel, The Water Babies - is the focus of this 4.5-mile walk, which comes courtesy of the Yorkshire Dales National Park Authority.

Surrounded by stunning scenery, the site also takes in Tarn Moss, a 15 feet deep peat bog, which is estimated to be about 12,000 years old; Tarn Fen, a calcareous fen, one of just a few such remaining sites of its kind in Britain; upland hay and wild flower meadows; limestone pavements, and an upland Ash woodland.

Its rich heritage of scientific interest dates back to the mid 1800s. In fact there is evidence to suggest that Charles Darwin visited the Malham Tarn estate in the late 1800s to investigate the impact of sheep grazing on heather.

Observant visitors may well wonder why the waters of Malham Tarn do not simply sink in to the ground given the limestone scenery which surrounds them. The reason is that the tarn actually lies on a bed of slate, displaced by the Craven Fault.

Instead the water flows southwards and disappears underground where it meets limestone at Water Sinks. It then reappears not as was originally thought at the base of Malham Cove, but at Airehead Springs, south of Malham. This is known as the source of the River Aire.

More walks in the national park can be viewed and downloaded from yorkshiredales.org.uk

Step by step

1. Leave the car park taking the Pennine Way path towards Malham Tarn, England’s highest lake. Follow the obvious grassy path next to the Tarn. This path leads to a gravel track around the Tarn National Nature Reserve.

2. The track heads through pleasant woodland belonging to Tarn House - a Field Studies centre - and leads around the back of the house. A National Trust Information Board provides a brief history of the house and site.

3. Continue on the track and pass the house, look out for a view point to the left - providing excellent views across the Tarn. A little further on the track a bird hide provides a bird watching point. Continue ahead past the cottages and look out for a track on your left. Follow this for a short while until you reach the road at a gate.

4. Turn right and walk along the road. After 300 metres, at the first road junction, take the left fork signed to Malham. Continue along this road, passing High Trenhouse on your right. Go across the crossroads and take the gate or stile on your left to cross the open field and head towards the smelt mill chimney (1815).

5. Take the faint path straight ahead from the chimney, following the waymarkers for about 100 metres to the corner of the field. Continue with the wall on your left, to another wall at the brow of a hill. Go over a stile and head straight forward, as the land begins to descend bear left.

6. At the foot of the hill a track leads to a gap in the wall to your left, signed public bridleway. Follow the path across Dean Moor until you reach the road at Water Sinks.

Distance: 7km (4.5 miles)

Time: a minimum of two hours

Parking: Informal car park north-west of Malham Tarn.

Toilets: Malham National Park Centre

Refreshments: cafés, pubs and shops in Malham village