watchtower; observation tower; lookout
A tower or elevated structure used for keeping watch, often in historical or military contexts.
They were watching the enemy's movements from the castle's watchtower.
Out-dated kanji form; 樓 is the kyūjitai of 楼.
Compound of 望 (bō, 'look far, hope') + 楼 (rō, 'tall building, tower'). The exact historical derivation is uncertain, but the spelling is conventionally associated with a tower for observation.