Despite containing only relatively small molecular components, the structure of [Eu(H2O)(9)](1.5)(CTV)(6)(CH3CN)(5.5)(H2O)(7.5)[Co(C2B9H11)(2)] (4.5) (C191H337.5B81CO4.5Eu1.5N5.5O57, a = 54.590(2) Angstrom, b = 37.5788(17) Angstrom, c = 31.8067(14) Angstrom, beta = 116.573(2)degrees, monoclinic, C2/c, Z = 8) is of an unusually large size and level of complexity, with an intricate hydrogen-bonding network formed between lanthanide aquo ions, water, and the small host molecule cyclotriveratrylene (=CTV). The 3D hydrogen-bonded network structure that results is unique and too complicated to apply the usual topological analysis. Instead a simplified model using structural subunits is described.