The lights slowly brighten and the children fall silent, then gasp. In front of them is a 100-foot high, underground cascade of what looks like a pale, toffee-coloured rock waterfall, though it's unmoving, frozen in time in this dark, clammy place deep underground.
"Who's going to be brave and touch it?" encourages the guide, Lynne Osgathorp. The group of Year 2 children from Weare C of E first school jostle forward to try. "What does it feel like?" she asks. "It looks slimy, but it's not actually slimy. It's pink," observes one child. "It's brilliant," says another. "It's spooky," says a third, casting an eye round the engulfing shadows. The sunny morning feels a long way away.
The venue is Cheddar Gorge, in Somerset, home to cheese, cider, and a 40,000-year legacy of cave-dwelling. But the caves themselves have been here much longer than that. "There are more than a hundred caves," says Lynne. "This one, Gough's Cave, is the biggest. People once lived in here - can you see the skeleton?"
The children peer in. "Before that, it was an underground river," she continues. "See the big swirls over our heads. They were carved out by water." This occurred 100 million years ago.
Year 2 teacher Felicity Gibb is pleased. "There are many links here with work we've been doing," she explains. "We've been looking at the local environment, at countryside, rocks and rivers, so that's a geography link; they will be writing a report for a literacy assessment; and in science we've been looking at different materials."
The children note that the rock is called calcite flowstone; and they can't wait to see the famous witch. "Turn around. Can you see the shadow of her big black cat?" asks Lynne. Avoiding dark puddles on the ground, small feet in sturdy trainers shift position as they look.
Managing the visits of hundreds of school students every week is a full-time job for the 40 trained staff at Cheddar Gorge. Many come to study the geology and geography of this stunningly spectacular site with its huge ravine and sheer cliffs hundreds of feet high, its network of caves and its singular ecosystem.
Others come to look at tourism, or at Cheddar's history and human prehistory, which dates back to Neanderthal times and is explained in a detailed state-of-the-art exhibition across the road from the caves, opened in 2005 and supported by living history displays.
Weare's Year 2s are more interested in meeting Stone Age man himself, in the person of living history actor Roger Chalwin. They watch with fascination as he makes a fire, chips flints and builds a fish trap outside his hut. "I wouldn't have liked to live here then," says seven-year-old Rebekah thoughtfully. "It would have been too cold in winter."
A dedicated education room accommodates talks, activities and excess baggage. Year 2 settle down on the cafe terrace with their lunch boxes, while staff buy coffee. If you like, you can visit the Crystal Quest, a cave fantasy adventure peopled by red-eyed orcs and fallen knights. Or you can book an open-topped bus tour up the valley between vast, sheer grey cliffs which loom high on either side. The Victorian hymn Rock of Ages was written not far away; it seems a reasonable response to this extraordinary landscape.
"Cheddar is always a good visit," says Felicity Gibb, as she and the children walk up Jacob's Ladder, 274 steps carved in stone to the top of the cliffs, at the end of the day. There they climb a tower and look out over the flat Somerset Levels far below.
"I can see Cheddar Reservoir," says six-year-old Daisy. "I can see everything in the whole world," counters Terri, her friend; and they run off through the sunny woods to play Palaeolithic hunters.
www.cheddarcaves.co.uk; contact education officer Bob Smart, tel: 01934 742343 to discuss your requirements. Open 10.30am-5.30 pm. Free coach parking and school room. Gough's Cave and Cheddar Man exhibition, pound;5 per student, one adult for every 10 students free; all attractions, excluding tour bus, Pounds 6.50; gorge tour bus (March to September) pound;1 extra. Downloadable teachers' Discovery pack with factsheets