Angkor, the sprawling archeological remains of an ancient Khmer city, attracts some two million visitors each year. The 390-square-mile site is packed with crumbling temples and hidden gems, but no temple sees more visitors than the famous Angkor Wat. And yet, despite the multitude of eyes passing through those ancient halls each year, no one had managed to spot the hidden paintings.

Around 200 paintings, some simple and some intricate, cover the temple's walls, experts have discovered. The big reveal was made by art expert Noel Hidalgo Tan, who was working at the site and spotted odd traces of reddish paint on the wall one day during his lunch break, LiveScience reports. Tan took some photos and didn't think much else of it. When he later uploaded the images to his computer and played around with them using a color-enhancing technique called decorrelation stretch analysis, he was shocked to find an entire menagerie of detailed imagery. Here's LiveScience:

The digitally enhanced pictures revealed paintings of elephants, lions, the Hindu monkey god Hanuman, boats and buildings — perhaps even images of Angkor Wat itself. One chamber in the highest tier of Angkor Wat's central tower, known as the Bakan, contains an elaborate scene of a traditional Khmer musical ensemble known as the pinpeat, which is made up of different gongs, xylophones, wind instruments and other percussion instruments. In the same chamber, there's an intricate scene featuring people riding horses between two structures, which might be temples.

Some of the simpler images, Tan and other experts think, might be from visitors who continued to drop by Angkor after its 15th century decline and eventual abandonment. But the more elaborate murals, the team thinks, were officially commissioned. Because some of the images seem to hint at Buddhist themes, Tan thinks they might have been painted between 1528 and 1566, when King Ang Chan attempted a last ditch effort at restoring and reopening the temple as a pilgrimage site, LiveScience reports.

See photos of more of the paintings on LiveScience.