Underground Tunnels - Any Use?

I was chatting to an electrician yesterday who was talking about the city's underground tunnels most of which I believe are from the war - bomb shelters etc. Could they be of much use? Apparently BT have made some use of them.

Not many of them would be of much use, I should imagine.

The BT one was built to take cables up Westgate Street when Stadium House was erected. I don't think it's in use any longer.

The medievil tunnel under Greyfriars would probably be pretty unstable while the canal tunnel under the city centre has long gone.

The only others I'm aware of are the docks feeder culvert under Churchill Way which still provides water to the docks and the air raid shelters in the castle which contain a small museum.

There's also the underwater pedestrian tunnel from the Sports Village to Penarth - its beginning and end were bricked up in the 60s but it's still there (probably flooded and totally unusable)

EDIT: Definitely flooded, they flooded it intentionally in the 70s to stop people trying to sneak in. It was drained in the 90s to be assessed and found to still be in good nick, with no major breaches. It would have cost £1m to return it to service then, but the money was never found for the project.