After climbing the Mount of Olives, we walked to the city of David (the old old city, North of and adjacent tothe current old city), and went into Hezekiah's tunnel (also Siloam tunnel). Hezekiah built this tunnel to make the water supply secure. It leads from the Gihons spring to Siloam's pool. It's just wide enough for one man. The height varies a bit. Sometimes you can stand, sometimes you have to bow for a while. Basically you walk 533 metres through the dark if you turn of your flash light. Which the kids did, they wanted to walk through the dark. Not for claustrofobic people!
The water is between 20cm to about 55cm or so, so you wade through water.