cavernous, voluminous

broad, wide

big, biggish, bulky, considerable, generous, goodly, grand, great, handsome, hefty, hulking, large, largish, outsize (also outsized), overscale (or overscaled), oversize (or oversized), sizable (or sizeable), substantial, tidy

Brobdingnagian, Bunyanesque, colossal, elephantine, enormous, gargantuan, gigantic, herculean, heroic (also heroical), Himalayan, huge, humongous (also humungous), immense, jumbo, king-size (or king-sized), leviathan, mammoth, massive, monolithic, monstrous, monumental, mountainous, pharaonic, prodigious, staggering, stupendous, super, titanic, tremendous

expansive, extended, extensive, vast

boundless, limitless, unbounded