The continent is split apart by a dense area of mountains, covered in glaciers. Any travelers who with to go from one part of the continent to the other would either have to cross the mountains, or go around them by boat, which brings its own set of problems many would rather avoid.
Given the adverse conditions in the mountains, many trails are plagued by frequent snowstorms, much to the detriment of the travelers. Luckily so, the trail goes along several larger cave systems, which happen to be between 15°C and 20°C (59°F and 68°F respectively), which is a boon in comparison to the frosty negative temperatures outside.
The caves are used by travelers to sleep or eat, and some vendors even set up semi-permanent stores to sell goods to those daring to cross the mountains.
Curiously enough, the temperatures are not caused by people trying to heat the cave by conventional means (e.g. camp fires, etc.). Why are the caves in such a high temperature year round?
I've looked into geothermal heating, but I was unable to say for sure if a near geothermal source (e.g. a dormant volcano) was able to deliver such a strong rise in temperature (~20-30 °C) in a way that doesn't have unwanted side-effects (e.g. sulfur gasses in the case of a volcano) .