Loch Torridon is a sea loch carved by ice. The glacier that ground out this fifteen-mile gouge in the western Highlands left behind a fjord-like trench with two sections - Upper Loch Torridon to the east, joining Loch Shieldaig at Rubha na h-Airde Ghlaise, and the main western basin of Loch Torridon proper running out to the Inner Sound. The mouth lies between Rubha na Fearna to the south and Red Point to the north. Smaller inlets - Loch a' Chracaich, Loch Beag - notch the southern shore of the outer loch. Islets dot the water. Eilean an Inbhire Bhàin, Eilean Dùghaill and Shieldaig Island sit in Loch Shieldaig; tidal Eilean à Chaoil and Eilean Cnapach in Upper Torridon; Eilean Mòr, Eilean Tioram and the Sgeirean - skerries - further out. The Gaelic name Thoirbhearta shares a root with Tarbert, indicating a place where boats were once dragged overland.

The Torridon Hills are not the highest mountains in Scotland but they are arguably the most dramatic. Liathach rises like a fortress wall, its terraced quartzite tops visible for miles. Beinn Eighe gleams white-grey in the right light. Beinn Alligin shows its serrated ridge of pinnacles, the Horns of Alligin, to anyone climbing from the loch. All three are over 900 metres. What makes them special is not height but composition: red and chocolate-coloured Torridonian sandstone, laid down by rivers and lakes a billion years ago when this part of the world was a barren landscape near the equator. The white caps on some summits are Cambrian quartzite, deposited some 500 million years later. Beneath all of it sits Lewisian gneiss, the basement rock of northwest Scotland - three billion years old, hardened by metamorphism, scoured smooth by ice. The Torridon Hills sit at the cusp of unimaginable time.

Torridon village stands at the head of the loch, ringed by the Torridon Hills. Walk down to the shore from the road and the mountains close in around you like cathedral walls. Diabaig and Wester Alligin and Alligin Shuas sit to the north along the loch's bend, and Shieldaig - meaning herring bay - stands to the south on its own small loch, its single curve of white cottages still pointed at the water. Redpoint marks the northern edge where Loch Torridon meets the Inner Sound. None of these are large. None ever were. The terrain does not allow it: too steep, too stone-strewn, too poor for anything beyond grazing and the sea. The 1999-2004 Scotland's First Settlers archaeological project found 129 new sites along Loch Carron and Loch Torridon combined - eight new ones on Torridon itself, suggesting the loch was actually quite intensively occupied in the Mesolithic. Of twelve caves and rockshelters examined, four showed evidence of human use. Prehistoric people, like modern ones, knew a good loch when they saw one.

Today Loch Torridon's economy runs on prawn and shellfish fisheries, salmon farms and industrial mussel production. The most distinctive catch is langoustine - the small clawed lobster known on Spanish menus as cigala and on French ones as langoustine, fished here by baited creels. Lines of up to 120 creels, each baited with herring or prawn, sit on the seabed for at least a day before the boats haul them back up. Most of the catch leaves the loch for Spain. Some sells locally to restaurants in Plockton and Ullapool. The fishery once held the Marine Stewardship Council's sustainable seafood certification, but the council suspended that certificate on 11 January 2011, after increased fishing pressure from creel boats that had not signed up to the voluntary code of conduct. The langoustines kept coming up. The certification stayed suspended.

Loch Torridon is one of those places where the weather is the show. Cloud rolls in from the Atlantic and snags on Liathach's quartzite tops, then peels away to reveal the mountain still standing there, indifferent. Late afternoon light turns the Torridonian sandstone the colour of warm rust. Winter brings snow on the high tops and Northern Lights on the clearest nights, the same loch surface mirroring auroral green when the sky cooperates. Beinn Damh rises across Upper Loch Torridon from the village, and any climb that gets you above 500 metres opens out the entire Inner Sound, with Skye and Rona and Raasay arrayed to the west like a chart spread out for inspection. This is the kind of landscape that does not need anything added to it. It just keeps showing you what stone and water and weather can do when given a billion years to practise.