noun
underwater observation tower
A tower built in the sea with underwater windows for viewing marine life; often found at tourist spots.
白浜の海中展望塔から、色とりどりの魚が見えます。
From the Shirahama underwater observation tower, you can see colorful fish.
Compound of 海中 (かいちゅう, 'in the sea') + 展望 (てんぼう, 'observation') + 塔 (とう, 'tower').