Longman Dictionary of Contemporary English
WordNet
n. a structure commanding a wide view of its surroundings [syn: lookout, lookout station, observatory]
Wikipedia
An observation tower is a structure used to view events from a long distance and to create a full 360 degree range of vision. They are usually at least tall and made from stone, iron, and wood. Many modern towers are also used as TV towers, restaurants, or churches. The towers first appeared in Germany at the end of the 18th century, and their numbers steadily increased, especially after the invention of the elevator.
Observation towers that are used as guard posts or observation posts over an extended period to overlook an area are commonly called watchtowers instead.
Usage examples of "observation tower".
Even before he reached the crest of the island, he could make out the glassed-in observation tower, a narrow deck running around its outer edge.
The gate bastion had a solid three-story timber observation tower as well, with the blue and silver Starburst banner flying from the peak.
Just before the murder, you rode the escalator to the observation tower on top of that amusement pier contraption.