In 1923, guided by the light of four candles stuck in the brim of his bowler hat, Christopher Long scrambled into a hole in the side of Ingleborough, one of Yorkshire's Three Peaks, and came across a maze of underground caves and passages. Formed over thousands of years by the erosive action of an underground stream on the soluble limestone rock, they run for nearly a mile into the mountain's heart, narrowing into claustrophobia-inducing tunnels and opening into vast caverns of stalactites. Today there is no need for candles: White Scar Caves, as the complex is now known, is paved with footways and lit by a generator. The guided tour is one of the main tourist attractions in the Yorkshire Dales and visitors now number more than 60,000 a year.
Over the years, disparate buildings - ticket office, manager's house, a cafÚ and WCs - have sprung up at the side of the cave entrance to accommodate visitors. The owner asked local practice Mason Gillibrand Architects to come up with ideas which would unify the buildings and also give visitors some protection against the harsh weather - they were often soaked while waiting for the next tour. (The caves are open all year except occasionally in winter when torrential rains flood the system and pour out of the entrance).
The logical solution was a canopy that would link the buildings and give sheltered waiting space. But the design was also led by the site and its climate - this was not the place for lightweight steel and glass. 'If you live in the south, it's hard to imagine what conditions are like up here in winter, ' explains project architect Richard Wooldridge.
'The site is well over 300m above sea level and on a clear day you can see the Irish Sea and experience the full force of south-westerly gales. In winter, blizzards often block the cave entrance with over a metre of snow. It's just another world.' The new canopy is elemental and solid;
a timber deck with a green turf roof which blends with the hillside above, so that it seems to flow over the assorted buildings.
Seen from the road and car park the canopy metaphorically 'extends' the mouth of the cave, radiating out from the rock to act both as an invitation and a shelter. Similarly, from a distance, particularly from the hillside on the other side of the valley where visitors walk up the famous 'Waterfalls Walk' from Ingleton, the canopy appears simply as an opening in the hillside.
To reach the cave, visitors park their cars and climb a new limestone staircase to the edge of the canopy. To one side is the cafÚ, which has been extended; to the other side is a new resource centre, an extension to the cave manager's house. To the back of the canopy, set hard against the rocky mountainside, is the single-storey ticket office which has been rebuilt and clad with limestone to help support it.
The canopy had to resist wind uplift but, because it sits in a slight hollow in the mountain-side, flanked by existing buildings, the need to accommodate snow-load was even more critical. The timber deck is covered with a two-layer turf roof system with 45 tonnes of soil and grass - heavy enough to resist wind uplift - supported by glulam beams. Eight 450 x 135mm tapered beams rest at the rear on the ticket office and fan out imperceptibly towards the main entrance opening. A further four beams, set at the side and further back, shelter the entrance to the cave itself.
The canopy is a shelter; once inside it you look back and realise that it also acts as a frame to what must be some of the most magnificent scenery in England.