On Monday 30 August, a pair of Scottish walkers completed a route following what's thought to be the longest straight line in Britain without crossing a road.
High point of the route was the summit of Beinn a'Bhuird at 1197m, while the low point, figuratively, sounds like all the heather they had to plough through...
A fine achievement but I do feel that the use of the term 'flatlining' is, perhaps, rather inappropriate.
flatline
slang To die or come very close to death. The "flat line" in question is a straight, horizontal line on an electrocardiogram or electroencephalogram indicating a lack of heart or brain activity (as opposed to the peaks and valleys displayed as a result of measuring the vital signs of a living person).