(n.) a steep hillside path
A path that steeply climbs up the side of a hill is a bostal, or borstall.
(FYI that’s different from borstal in the sense of an institution for young offenders, which takes its name from the location of an early reformatory house in the village of Borstal in Kent, England.)
This bostal is a dialect term, the earliest record of which dates from the late 1600s. Like a lot of regionalisms, the etymology of bostal is something of a puzzle, and with little textual evidence to go on the best we can aim for is an educated guess. The Oxford English Dictionary plumps for a compound of two Old English words: beorh, meaning ‘hill’ (the origin of barrow), and stigel, meaning ‘stile’ (a word that survives in English to this day). And just as a stile lifts you over a scalable fence, a bostal takes you up a scalable hill.
An alternative there here is that the second element isn’t quite so imaginative. Instead of stigel, it but could instead derive from another Old English word, steall, essentially meaning a standing, a position, or a specific location (which is the origin of the word stall in that sense in English today).