What the title says.
There is no great sword & sorcery adventure without exploration and discovery. Exploration requires wilderness, and wilderness implies a negation of the World-Building (“everything needs to be mapped and known”) ethos in sff. Adventures require tension, and tension is impossible if everything is mapped, if civilization is dominant, or if the protagonist can go back to their HQ to resupply and rest. Hence, a vast blank space on the map and danger from wich you cannot escape are required: dungeons, caves, ruins, or being trapped inside a magician’s tower. The hero, if he wants to survive, has no other option but to keep going down.