Last Thursday there was a conference at the City of David Excavations which is located just outside the current Old City walls, down in the Kidron valley. It is the location of Jerusalem from David's reign (II Sam 5:9) and is also talked about in II Chronicles 32. The Shiloach inscription that was found at the site related back to vs 30 " This same Hezekiah closed the upper outlet of the waters of Gihon and directed them down to the west side of the City of David..."
The point is that part of the events included a tour of the underground water systems. We actually walked along where Hezekiah's men redirected the water and crawled through the tunnels that they used.
Best I can do is point you the the web site the foundation has built. It's pretty amazing.
City of David website
Here's a couple of pictures. One taken inside a naturally formed cave along the water route and the second is of the outside near the site looking up towards the Mount of Olives. The gold roofs you see are on the Russian Orthodox church.
