Something that is stupendous is surprisingly impressive or large. He was a man of stupendous stamina and energy This stupendous novel keeps you gripped to the end. surprisingly large or impressive = magnificent (stupendus, from stupere; STUPID)
so great in size or force or extent as to elicit awe; "colossal crumbling ruins of an ancient temple"; "has a colossal nerve"; "a prodigious storm"; "a stupendous field of grass"; "stupendous demand"