high, high-rise (BrE), lofty (literary), massive, tall
two-storey/two-story, 20-storey/20-story, etc.
30-foot, 100-foot, etc.
round, square
ancient, Gothic, medieval
fortified
ruined
control, guard, lookout, observation, watch (usually watchtower)
Armed guards manned the lookout towers.

bell, clock
cooling, water
cell, cellphone (both AmE)
radio, television
apartment, office, residential (all esp. AmE)
conning (esp. BrE)
the conning tower of a submarine

castle, cathedral, church
glass
ivory (figurative)
academics sitting in their ivory towers

collapse, fall
stand
the spot where the towers once stood

block (BrE)

Tower is used with these nouns as the subject:
cliff, mountain, peak