Even if you live in Scotland, there is something special about the moment, heading north, when you realise you have reached the Highlands. It comes somewhere not long after the Pass of Killiecrankie, when the mountains become bigger, the distances greater, the population more sparse. The very air smells different as you cross the boundary into the Cairngorms National Park (tussock grass, I reckon, together with hints of heather, ozone and pine).