The Utilidors under the Magic Kingdom at WDW are well known, but fewer people know about the original Utilidor, the Tomorrowland Tunnel at Disneyland.
The tunnel runs from the back of Alpine Gardens to a backstage area next to Innvoventions and provides access to the central core of Innoventions, the Terrace Stage, the Terrace trash compactor, the Tomorrowland Terrace basement, storage and, of course, Alpine Gardens.
For a number of years plans to build a branch to the Lunching Pad were considered but, ironically, a tunnel wasn't built until after the Lunching Pad was closed. And the tunnel that was built (for the Rocket Rods Queue) didn't even connect to the Tomorrowland Tunnel. I wonder what the Rocket Rods tunnel is used for now?
Various conduits run the length of the tunnel to provide water, electricity and telephone service to Tomorrowland. Oh yeah, and Coke Syrup! There are two huge stainless steel tanks behind Innoventions that are used to store Coke Syrup for Coke Terrace via a tube that runs through the tunnel.
Edit: Jason requested a picture of the Tomorrowland Tunnel, so here it is:
I slay me. Stolen without permission from another website:
This view would be looking towards Fantasyland and I think this was taken near the freight elevator behind Innoventions. It was pretty common for water to pool on the floor of the tunnel at various points. Tomorrowland Terrace had a golf cart that the receiving crew would use to carry stuff. I believe rolling pallet jacks were also used. If you look closely you can see guard rails to protect the piping from bad golf cart drivers!
It's hard to identify anything because of the small size of the picture, but I think the stairs to Innoventions are on the left just in front of the puddle.
The tunnel has at least one bend and maybe two.
The tunnel was also used by Custodial to haul trash from the Tomorrowland Terrace trash compactor.
The original intention may have been to extend the tunnel at some point in the future since after the Tomorrowland Terrace the tunnel has no real purpose (I only recall some fenced off rooms containing machines of some sort).