"colossal achievement" is a correct and usable phrase in written English.
It is often used to describe a significant or impressive accomplishment or feat. Example: Winning the championship for the third year in a row was a colossal achievement for the small-town basketball team.
That is a colossal achievement.
The colossal achievement of this series really is something to wonder at.
But Perlman's novel is a colossal achievement, a complicated, driven, marathon of a book.
It's a scream - in both senses, of antic uproar and wailing humanity - and a colossal achievement for British writing.
The Clements Checklist of Birds of the World is a colossal achievement and a fitting tribute to a man who devoted a lifetime to the study of birds and nature.
It is also a colossal achievement, gathering thousands of shreds of evidence from a vast span of sources to trace the fates of English Gypsies from their first arrival among us until now.
These were colossal achievements in which constancy and imagination coalesced.
Despite their colossal achievements, there was always a need for justification, for the comfort of association.
Though already awed by Beethoven's colossal achievements, Brahms put his concerto out into the world with seeming bravado — as if to say, "My First Piano Concerto is longer, harder, and meatier than Beethoven's" — and took up his predecessor's gauntlet by composing it in D minor, the key of Beethoven's titanic Ninth Symphony.
Gray's subject is the pursuit of a truer, better self, one that's imbued with and inspired by the colossal achievements of the past, a self-accomplishment that's distinguished from the petty rounds of daily negotiations and drawing-room squabbles.
Though already awed by Beethoven's colossal achievements, Brahms put his concerto out into the world with seeming bravado as if to say, "My First Piano Concerto is longer, harder, and meatier than Beethoven's"—and took up his predecessor's gauntlet by composing it in D minor, the key of Beethoven's titanic Ninth Symphony.
