Ancient (structures) are that are very, very old. Earthquakes can damage them or destroy them. Even when (struck) by great earthquakes, some ancient structures are so (solid) that they are never completely destroyed. Explorers (report to) the authorities when they find an ancient structure on land or under the sea. These old structures can be dangerous, and it is always a (bold) move to explore them. The explorers will often take a (piece) of the remains, just a of the building that they can study later.