question:  Why were the Ryzgas not afraid that someone might enter their mountain?
context: Dark was the Ryzga mountain and forbidding; steep were its cliffs and sheer its crevasses. But its outward perils could not compare with the Ryzgas themselves, who slept within, ready to wake and conquer.... Now, if her father and his kinsmen overtook them, it would be death for Var, and for Neena living shame. While she waited he spun a dream, attaching it to the crags that loomed over the pass, and to the frozen ground underfoot. It was black night, as it would really be when Groz and his henchmen reached this place; lurid fire spewed from the Ryzga mountain, and strange lights dipped above it; and for good measure there was an avalanche in the dream, and hideous beasts rushed snapping and ravening from the crevices of the rock. Both had heard of this place, and the ancient who lived there to keep watch on the Ryzga mountain, as a part of the oldest legends of their childhood; but neither had been here before. Var saw with some surprise that all the walls were sheathed in ice—warm to the touch, bound fast against melting by the Watcher's will. Behind them began a tinkling of falling water, thawed from the glacial ridges above to descend sheet-wise over the cave mouth, freezing as it fell into lengthening icicles. Hot food and drink were before them almost at once. "In the hollow heart of their mountain the Ryzgas sleep, as they chose to do when their world crumbled. "In my youth I penetrated farther into the mountain than anyone before, farther even than did the First Watcher. There were tyrannies before the Ryzgas, there was lust for power, and atrocious cruelty; but such tyranny, power, and cruelty as theirs, had never been known. "Because of them we must build with dreams instead of iron, and our only fire is that of the Sun, and even now, two thousand years later, the Earth is still slowly recovering from the pangs and poison of that age.
output:  They were convinced that no one would be able to penetrate the mountain without advanced technology
options:  They did not believe that anyone would want to return to a terrifying society that the Ryzgas left behind  They commissioned the Watcher to spin dreadful dreams about what might happen if people attempted to do so  They thought that their descendants would eventually die out without access to raw materials  They were convinced that no one would be able to penetrate the mountain without advanced technology