Go to Puebla, Mexico and look for a giant hill with a church on top. What you’re seeing is no ordinary hill. It’s actually the world’s largest pyramid.

No one knows who constructed it 2,300 years ago or if they knew the clay they used would help plants hide it from view. But one thing is certain, it was ridiculously hard to find. Cortés missed it when he invaded Cholula in 1519 and locals didn’t re-discover it until 1910.

Today, it’s still the largest monument ever constructed and is similar in structure to the Pyramid of the Sun. It’s about 9 Olympic swimming pools long and 1.3 pools tall and has almost twice the volume of the Great Pyramid of Giza, and a base that’s 4 times as large.

Archeologists have uncovered over 400 human burials in and around the pyramid, which suggests it was an important place of worship. But, experts say it was abandoned sometime in the 7th or 8th century. Today, it’s an attraction for tourists with a keen eye.