Scylla & Charybdis
Σκύλλα, Χάρυβδις
A six-headed monster on one side, a ship-swallowing whirlpool on the other.
They flank a narrow strait, so avoiding one means falling to the other.
Odysseus chose to give six of his men to Scylla rather than lose the whole ship.
"Between Scylla and Charybdis" still means choosing the lesser of two evils.
SourcesHomer, Odyssey