Yes, hollow islands. You'll find them at Halong Bay, Vietnam.
Halong Bay is definitely one of the world’s wonders.
Within the bay are 1,969 limestone islands covered with jungle vegetation. They rise up from the sea like moss-covered fangs. The whole effect is otherworldly.
The islands range from 160 to 330 feet high, and have sheer, vertical cliffs.
Some of the islands are hollow, containing huge grottoes. The largest grotto is called Wooden Stakes Cave and is comprised of three large chambers. French tourists from the 19th century decorated the grotto with graffiti.
Other islands contain lakes, some of them fully entombed within the island itself.
Geologists claim there are still hundreds, if not thousands, of caves, grottoes, and lakes hidden away in the islands and still waiting to be discovered.
Halong Bay was listed as a UNESCO World Heritage Site in 1994.
