What was the reasoning behind the Himalayas being a barrier in the medieval era?

I don't understand how the Himalayas were a barrier in the medieval era. Yes, the mountains are impassable without modern technology; however humans have inhabited the region for tens of thousands of years. Why didn't medieval era map-makers send groups of locals through the mountains (who were obviously capable of traversing the mountains) with horses, camels, and other animals to go past them to set up a trade route along the eastern coast of Asia (or even to find a water route if it exists)? It makes no sense for the Chinese to set up a Silk Road that goes through the entire continent every time to the Black Sea. This is especially true considering the Silk Road was established over 1,000 years before the medieval era.