structure vs observation tower

Other hyponyms of structure include airdock, hangar, repair shed, altar, arcade, colonnade, arch, area, balcony, balcony, bascule, boarding, body, bridge, span, building, edifice, building complex, complex, catchment, coil, helix, spiral, volute, whorl, colonnade, column, pillar, corner, quoin, cross, deathtrap, defence, defense, defensive structure, door, entablature, erection, establishment, false bottom, floor, level, storey, story, fountain, guide, card-house, cardcastle, cardhouse, house of cards, housing, living accommodations, lodging, hull, jungle gym, lamination, landing, landing place, lookout, lookout station, observatory, masonry, memorial, monument, hill, mound, impediment, impedimenta, obstructer, obstruction, obstructor, divider, partition, platform, weapons platform, porch, post and lintel, prefab, projection, public works, sail, offset, set-back, setoff, shelter, shoebox, sign, signboard, arena, bowl, sports stadium, stadium, superstructure, supporting structure, tower, transept, trestlework, vaulting, shipway, slipway, ways, wellhead, wind tunnel, honeycomb, balance, counterbalance, equilibrium, equipoise.