The morning after the fog sequence when Mac and Oldsen travel to Ferness was filmed on the B862 overlooking Loch Tarff. This is around 4 miles north of Fort Augustus on the east side of Loch Ness.
There is space to park cars near the north end of the loch and from there it is less than 175m to the filming location. Alternatively there is a couple of passing places up the hill around 25-50m distant.
The fog seen in Local hero is not unusual in the area. On the day I visited I travelled north up the A9 in brilliant sunshine and clear skies but as soon as I went south near Loch Ness it was dense fog for mile after mile all the way to Loch Tarff.
Luckily the fog cleared up just long enough for some photos before it rolled back again.