Reviving an old-ish thread. When I was in high school I found a drainage tunnel (in Burnaby near where I live)
and I never got the courage to venture far into it. There's an input on the left side down a ways. I tried taking a pie plate and putting cardboard on it and lighting it and sending it down, it kept going strong for a while then suddenly went out and not from water, like a strong draft. I could hear it go for a while scraping on things before going down what sounded like a sloped part. Now towards where the pipe goes there is a development being built where there used to be a green space. Not sure if it will get dug up soon or not. It may or may not be of interest to anyone.