We just discovered a reef taller than a skyscraper.

How could it stay hidden? Science magazine celebrates the first big reef discovery in 120 years… and it really is big:

At 500 meters tall, the reef surpasses the height of the Empire State Building and the Shanghai World Financial Center. Researchers made their discovery during a 3D mapping exercise of the northern Great Barrier Reef sea floor, part of a yearlong effort to explore the oceans surrounding Australia. With a 1.5-kilometer-wide base, the reef tapers to a point just 40 meters below the ocean’s surface, the Schmidt Ocean Institute announced in a press release this week.

You can read the release here, and see video of the detached reef – which is not connected to the Great Barrier Reef, though part of the same system – here.