More conventionally, springs, caves, shores, rivers, volcanic calderas—"a huge crater of an extinct volcano... another symbol of transcendence"—fords, passes, crossroads, bridges, and marshes are all liminal: "'edges', borders or faultlines between the legitimate and the illegitimate". Oedipus (an adoptee and therefore liminal) met his father at the crossroads and killed him; the bluesman Robert Johnson met the devil at the crossroads, where he is said to have sold his soul. Major transformations occur at crossroads and other liminal places, at least partly because liminality—being so unstable—can pave the way for access to esoteric knowledge or understanding of both sides. Liminality is sacred, alluring, and dangerous.