Sometimes stories get exaggerated.
Sometimes, they turn out to be true. A team of archaeologists has found an ancient pilgrimage site...a cave with vapors so foul that it was said if you tossed a sparrow in it would drop dead instantly.
They had to be careful - the cave, site of a hot spring, still produces enough carbon dioxide to kill birds. The stories were apparently true.
A lot of the time we dismiss myths as not possible, but a surprising number of them carry within them a strong kernel of truth.