Ancient monument twice the size of Stonehenge found nearby . Thought to be between 5000 and 12,000 years old . Archeologists believe it was built on land then later submerged . The truth is we do n't know how it was constructed , what its exact age is , how it was used , or how long ago it was used . Unknown as to site 's purpose ; may be ceremonial structure or huge ramp .
Ancient monument twice the size of Stonehenge found nearby . Thought to be between 5000 and 12,000 years old . Archeologists believe it was built on land then later submerged . Unknown as to site 's purpose ; may be ceremonial structure or huge ramp .