The site is near a water source. During siege times, they had an underground tunnel to it, which you can tour today. James Michener wrote a book based on this site called "The Source". It's pretty educational and interesting. The premise for the book is about archaeologists finding little objects of one kind or another on each level of the dig. Michener then writes a story about how each object came to be deposited at that layer.
The Megiddo water tunnels to the spring outside the fortifications were built under the direction of Joshua. Very impressive to walk around such ancient ruins.