That tunnel is for whimps! ;0)
Just above the Falkirk Wheel, on the Union Canal, there are two canal tunnels. The first is quite short and quite well lit. The second is long, I'm guessing but maybe about a mile. So on the cobbled towpath you've got a stone wall on one side and and hand rail on the other between you and the canal. Depending on the time of day it can be pitch black in the middle of the tunnel, you can't see your hand in front of your face. You are not supposed to ride through it for obvious reasons. The cobbles are wet, water pours out of the roof at parts, if you fell over you might well go over the hand rail into the pitch black water and the only thing to keep you going straight is the light you can fleetingly make out on the top of the hand rail!
The first time we went through this tunnel we all got off and walked, there was about eight of us. We cycled into the tunnel but very soon started getting disorientated and bumping into each other etc so got off. Even then as we all walked through it was still hard.
There were just three of us the last time we went through it and we cycled it! I'll be honest, I really didn't like it. The other two were in front of me and they just kept peddling. We'd been against the wind for miles, we were fed up and we just wanted to get back but if it hadn't been for them I would've gotten off and walked. The only reason I stayed on the bike was that I didn't want to end up way behind.
As it was I went slower than them. It was very disorientating and you had to try and look at different things to keep you straight. If you just looked at the light at the end, or at the rail, you got kind of dizzy and wobbly. It wasn't nice.
The tunnel now has lights, but it's still scary. Now that is a f****** tunnel! ;0)