The high-nuclearity polyoxothiomolybdate [H8Mo84S48O188(H2O)12(CH3COO)24]32- has been prepared and characterized by single-crystal X-ray crystallography and spectroscopically (1H NMR, IR and Raman, UV-vis). The solid-state structure reveals an unprecedented and intriguing arrangement comprising a nanoscaled anionic cube. The surprisingly open structure of this {Mo84}-type cubic box features a large inner void, accessible via its six open square faces of about 9 Å in diameter. Importantly, this molecular system appears highly functionalizable owing to the presence of 24 exposed exchangeable acetate ligands.