Sagot :
The world longest navigable under river is found in the Philippines
Puerto Princesa Subterranean River National Park
Explanation:
The Puerto Princesa Subterranean River National Park is a stunning natural place about 50 km north of Puerto Princesa City, in the St. Paul Mountain Range. It features the world's longest navigable underground river and one of the most impressive cave systems in the world.
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Answer:
the Puerto Princesa Subterranean River National Park