Don't worry, it's easy to find the boulders, but you need to do some exploring amongst them to find the "secret" cave. It will only hold 6 at the most, and that's cramped. I'll give you good directions, but I think it's important for people to find things for themselves.

Get out your English Lakes North-Western area 1:25,000 scale map. Park at Stonethwaite grid ref. 262137. Walk past the Langstrath Inn and keep on the south side of the beck all the way as it turns south into Langstrath. I hope it's good weather, as you'll have an incredible view, framed between the buttresses of Heron Crag and Sergeant's Crag to the east and the steep slopes of Glaramara to the west, of Bow Fell rising like a pyramid at the far end of the valley. It's called Langstrath for a reason; it means long valley and derives from the Norse language. Anyhow, carry on the west bank, passing the delectable pool of Blackmoss Pot, a favourite plunge pool. Carry on, my friend, for another few hundred yards. A track will be seen, rising diagonally up on the right (unless you go there when the bracken is fully grown, when you might have a problem finding it). This will lead to an area of huge boulders below and to the left of a vertical crag, amongst which the cave can be found. These are called Woof Stones and are marked on the map. This vertical crag will be below an obvious rock ridge which contains quite a bit of white quartz. The ridge itself rises in a series of steps to a few hundred feet below the summit of Glaramara and is an enjoyable and easy grade 1 scramble.

Happy hunting, and I hope this helps. By the way, be careful if you light a fire in the fireplace; keep an entrance slightly open, as ventilation is key to not dying of CO poisoning.

All the best,
TE.