here is a small map of the canal system i ve found and also a picture from google street maps of the start of the canal to give an understanding of the map.
I read up on this place alot before i went in myself last year, when it was first constructed it wasn't a tunnel system but in fact open to the air and as the city centre grew it was culverted over.
Here is a video of the rediscovery for those interested
http://www.youtube.com/watch?v=yQ3NP...=youtube_gdata
Rigy