Ein Koby, Natural spring in Jerusalem District, Israel.

Ein Koby is a layered spring in Nahal Kobi, a valley descending toward Nahal Refaim near Mavo Beitar. Water seeps about 4 m down at the contact between Dolomite of the Amindav formation and the impermeable Moza marl, and a 12 m tunnel cut along the water-bearing layer carries it into an underground vaulted chamber with a pool holding water all year. From there a roughly 17 m tunnel leads out to an open pool, and stone steps descend to the inner pool.

The site dates to the Roman-Byzantine period when people built sophisticated water systems. Later, an Ottoman-era structure was built above it, featuring a prayer niche oriented toward Mecca.

The spring reveals how past communities managed water for farming, channeling it through tunnels to pools beyond the chamber walls. This system shows the ingenuity of builders who adapted their methods to the local landscape.

Access is via stairs descending into the underground chamber, where light enters through an opening in the roof. Wear comfortable shoes and watch your footing on the uneven surfaces inside.

The 17-metre passage from the underground chamber is a low tunnel, not a vertical shaft: visitors crawl through it on hands and knees to reach the open pool outside. The water system was repaired over many centuries, and the concrete ceiling of the underground pool dates from the British Mandate.