So I’m lunching with my friends Chris and Gabe one day…

Gabe. He’s a man of many talents, tastes, trades and skills. Learn about him here: http://citysound.bohemian.com/about/
Just relaxing. Enjoying the spoils of life at one favorite little spot known as SuperBurger. Here is the modest meal otherwise known as The St. Helena:
And Gabe says, “so Jake, you’ve really never been in the tunnel beneath City Hall?”
“No, never” I answer.
“Well, let’s go. You want to see that tunnel now.”
It was just like that. A statement – not a question at all. And Gabe was right. He’s got me pegged. I wanted to see that tunnel.
“It’s amazing… there’s a point in the middle – about 30 steps worth – where you have no light behind, and no light ahead – you’re walking by feel – it’s awesome.”
“Once, in high school, we decided to setup and play [music, punk probably] down here.”
A handy map of the underground path: http://goo.gl/maps/gKdhk
…no, I do NOT condone you going yourself. That’s strictly prohibited.
Again… you definitely should not see this for yourself. Avoid the entrance on E street at all costs.

Creekmap by Google.
http://goo.gl/maps/gKdhk
the tunnel looks devoid of water. Where was the water the fill Prince Memorial Gateway?
There are three tunnels: North has Santa Rosa Creek water – middle (which we walked in) only has water when the creek level is above 2′ (heavier flow), and South is Matanzas Creek, which enters near Burbank Gardens, but exits with the other two at Prince. We hiked the middle tube.