Glencoe is a deep pass through the western Highlands of Scotland, and the walls that press in on the road are the inside of a volcano. About 420 million years ago a supervolcano here drained its own magma chamber, and the whole cauldron of rock sank along a ring fracture, dropping its core below the reach of erosion. That collapse is the only reason any of it survives, and geologists mapping the glen coined the term cauldron subsidence for it. Ice-age glaciers then cut a trench through the wreck. The A82 threads the floor of it, black cliffs close on both sides, and every bend brings you another waterfall, a shaft of light, or the road ahead going into cloud. At the eastern mouth the sharp pyramid of Buachaille Etive Mòr stands over the small white Lagangarbh cottage, the picture everyone takes. Further in, the Three Sisters drop into the glen straight above you, three great buttresses off the ridge.
Where the road runs along Loch Achtriochtan, a still morning gives you the tops on the water without a ripple, and in October the bronze bracken comes with them. The massacre is the other thing the glen is remembered for. In 1692 soldiers quartered with the MacDonalds as guests turned on their hosts, under orders to make an example of a clan late in swearing loyalty to the king. Three centuries on it still colours the place. For years the old Clachaig Inn kept a notice at the door reading No Hawkers or Campbells, and staff still field the odd real Campbell asking for a room. The brooding light has made the glen Hollywood's shorthand for wild Scotland; the road through the pass opens Skyfall, and Hagrid's hut was built here for Harry Potter. The best of it is off the road. You climb a steep, boulder-strewn gorge between the Three Sisters, and the ground suddenly levels into Coire Gabhail, the Hidden Valley. It is a wide, silent bowl ringed by peaks, and not a metre of it shows from the road below.