Begone, Fowl Creature.
This is a manuscript image of Hercules saving Hesione, from the 15th century Histoires de Troyes. Legend has it that Poseidon sent the sea monster because he, and his nephew Apollo, were not paid for their work they did building Troy. Hercules, apparently, saw Hesione's naked body chained to some rocks and fought the monster (but only after getter her father to agree to hand over four immortal horses in payment). The monster was covered in impenetrable scales, so Hercules killed the monster by getting himself swallowed whole, and then hacking his way out from the gullet. That's what this image is depicting.