One of the highlights of visiting the City of David is a trip through Hezekiah’s Tunnel. This tunnel was an incredible engineering feat and was constructed more than 3,000 years ago by King Hezekiah as he was preparing the city’s defenses against the approaching Assyrian army. He diverted the spring water of upper Gihon to protect the city’s water reserves and it served as Jerusalem’s primary source of water, according to the Bible. It was done by digging a 1,750 foot tunnel straight into the mountain. It is located in a major archeological site and functioning residential neighborhood in the Old CIty. Today, you can hike through knee-high water and learn about its history.