Wiktionary
no mean feat
n. (context idiomatic English) A laudable triumph of great difficulty.
Usage examples of "no mean feat".
It was no mean feat of horsemanship and stamina: the Chronicle says he rode by night and day.
He struggled upright, no mean feat with his hands bound behind him with leather cords.
The disorientation spell was cast as the wards fell, and the sudden transportation of the Death Dancers was no mean feat.
It was no mean feat to concoct a thing the size of a cigarette packet that would pour out a hundred times as much energy as its most efficient competitor.
It had been no mean feat to bring back a thorn-gem, and he had paid the price.