Herculean
Etymology
From Hercules (the Roman name for the Greek hero Heracles), famed for superhuman strength and for the Twelve Labors — a series of near-impossible tasks, from slaying the many-headed Hydra to capturing the hound of the underworld, imposed on him as penance. The adjective borrows the scale of those labors to describe any effort of extraordinary magnitude.
adjective · /hur-kyoo-LEE-un/
Requiring or displaying enormous strength, effort, or endurance.
What it names
A task or feat so demanding it seems fit only for a superhuman — use it for challenges that would exhaust anyone of ordinary powers.
Example
Rebuilding the archive from scratch after the flood was a herculean job that took the whole team a year.
Related idea
Arduous means simply difficult and wearying; herculean adds a sense of near-mythic scale, of strength beyond the normal human measure.