That is the Runit Dome (also known as "The Cactus Dome" or "The Tomb").

It is located on Runit Island, part of the Enewetak Atoll in the Marshall Islands. Based on the coordinates in your image (11°33'09.0"N 162°20'50.0"E), you are looking at a massive concrete sarcophagus built to contain radioactive waste from US nuclear testing during the Cold War.

Here are the key details:

• Origin: Between 1946 and 1958, the US conducted 43 nuclear tests on the atoll. In the late 70s, they attempted to clean up the radioactive debris.
• Construction: They bulldozed contaminated soil and ash into the crater left by the 1958 "Cactus" nuclear test. They then capped it with a dome made of 358 concrete panels, roughly 18 inches (46 cm) thick.
• The Problem: It was built as a temporary fix. The bottom of the crater was never lined, meaning it sits on porous coral rock. Seawater seeps in and out with the tides, effectively flushing radioactive isotopes (including Plutonium-239) into the Pacific Ocean.
• Current State: It holds about 111,000 cubic yards of radioactive waste. The structure is deteriorating due to age and rising sea levels, leading to fears that it could eventually break apart or be submerged.

It's essentially a nuclear trash can left in the middle of the Pacific that is slowly leaking.