Earlier quoted context omitted.
Much of the interior of Western Australia (an area 3x the size of Texas) can be divided into very few cells which essentially look near identical in all directions, coupled with few roads for the area and not much in the way of uploaded snaps coverage. There's a lot of flat lands with spinifex in certain areas (easily a couple of United Kingdoms in size) and even a touch of mesa won't help narrow a location down from…
Because seem like someone who might have an interesting answer: A GeoGuessr player, GeoWizard, has done a few “straight line challenges”, where he attempts to walk across a country in as straight a line as possible, usually planning beforehand with Google Earth and PostGIS. This got me thinking of what could fairly be thought of as “crossing”, since obviously you couldn’t describe e.g. walking from one side of Florid…
Some might then say that "crossing" that polygon is to travel that longest line across the greatest width.
This simplistically avoids the question of concave polygons, complex polgons with exclusions (the Vatican state is removed from the Italian contry bounds), polgon collections (the nation of Fiji has many islands and can be tricky to traverse on foot .. not forgetting that perhaps the longest diameter might be from one island to another with no other islands between).
There's also the challenge of parallel lines on a 2D 'spherical' manifold, the almost spherical abstract ellipsoid of earth (or very non ellipsoidal Geoid if we take a constant gravitation value as the surface). On such manifolds lines are Great Circles (more or less) and always intersect.
Still, lets just say you're looking for the longest walkable(?) great circle path across a country that might go outside that country and perhaps is best travelled by a crop duster at 80m ground clearance to avoid getting feet wet.
The challenge itself takes some posing.
Meanwhile, less abstractly, I do like a jolly that "crosses a country" in a manner accepted by a (Wo)Man on a Clapham omnibus.
eg: https://en.wikipedia.org/wiki/Robyn_Davidson only went "half way", but that was accepted as an epic crossing. https://thelongridersguild.com/stories/stef-gebbie.htm "only" crossed most of the E-W distance across the lower portion of the country, while https://www.abc.net.au/news/2021-04-03/french-woman-conquers... travelled North - South, the long bit, but not quite coast to coast ( https://en.wikipedia.org/wiki/Bicentennial_National_Trail ).