![Image](http://farm3.static.flickr.com/2371/2424017433_bbddbecc8d_b.jpg)
I've also got a better version of this picture, from the same edition of the ILN:
![Image](http://farm4.static.flickr.com/3225/2424834374_1239fa080f_b.jpg)
All accounts say that this station, from where passengers began their journey, was near the Sydenham Gate. Behind the train is the boiler house and to the right of the boiler house is the casing enclosing the fan. The pipe referred to would only have extended from the fan to a point just beyond the entrance to the tunnel, no more than a few yards, so it can have nothing to do with the "pipe" you referred to earlier.
Yesterday I had a look at the area you suggested might be the site of the tunnel, and took this photograph:
![Image](http://farm4.static.flickr.com/3095/2425496504_6238cc339e.jpg)
There is a barely perceptible shallow depression, from close to the path at the left of the picture, curving away towards the information centre in the centre distance. However, if you follow it, the depression continues round the cricket pitch, perhaps making a complete circuit. I'm fairly sure it is all that is left of a miniature railway ran round the pitch some years ago.