Durness to John o' Groats

A short signed path from a car park at the edge of Durness leads down to Smoo Cave, a combined sea-and-freshwater cave cut into the limestone cliffs — one of the larger sea caves in Britain, with a wide, easily walked outer chamber you can enter on foot for free, and a waterfall-fed inner chamber reachable by a short boat trip in summer months when water levels allow it. It's one of the few genuinely dramatic, easy-access stops on the whole route that costs nothing to see the main chamber.

East of Durness the road crosses the Kyle of Tongue on a causeway, with the option of the older, longer single-track road around the head of the kyle if the causeway is ever closed. Tongue village sits below Castle Varrich, a small ruined tower thought to occupy the site of an ancient stronghold of Clan Mackay — reachable by a waymarked walk of around an hour round trip from the village, with the ruin itself perched on a hilltop overlooking the whole kyle.

Between Tongue and Thurso the landscape flattens into the Flow Country, one of the largest expanses of blanket peat bog in the world — genuinely bleak in poor weather, genuinely huge-skied in good weather, and one of the windiest stretches of road on the route. There's little in the way of towns for a real stretch here; treat it as a driving-focused section rather than a stop-heavy one, and top up fuel before you leave Tongue if you're running low.

Thurso is Britain's most northerly mainland town of any size, with Scrabster harbour just outside it serving as the ferry terminal for Orkney. It's the last proper town before John o' Groats and a sensible place to fuel up and eat before the final short push northeast.

John o' Groats itself is a small harbour hamlet, not mainland Scotland's actual most-northerly point (that's Dunnet Head, a short detour west) — but it's the traditional end-to-end marker paired with Land's End, and the harbour building and famous signpost make it worth the stop regardless. Duncansby Head, just beyond, has better cliff scenery and sea stacks than the village itself if you only have time for one short walk here.