At the Dell end of Rock Park, there is a patch of grassland between Rock Park Road and the river with Three crack willow trees (one now dead) on it.

I've noticed a dark patch of vegetation on the slope down in the direction of the Car park. It can be clearly seen in Google Earth too, and seems to get darker in wet weather.

I wonder if there was something there that has since been demolished. An Air raid shelter Perhaps?, Or an old house? Or perhaps there was a spring there?

Has anyone else noticed this and been curious enough to find out?.

As a separate issue, many years ago before the New Ferry Hotel was demolished, a group of workers were laying a new gas main and between the Hotel and the car park (Ferry terminal as was) broke into a tunnel. There were steel rails a couple of feet apart and the suspicion was that at one time there might have been a tunnel leading to the hotel cellars where barrels of beer could have been conveniently rolled from the Ferry? Keen to get finished the gang filled in the void and coompleted the job, but I did see a photograph of it taken by a neighbour.

an anyone confirm the existence of this tunnel and its function?

One of these used to be there , down the slope towards river. I remember going in it as did all the kids. Dirty and smelly but it was our den ha... ww2 Pill Box by the way.

That might explain it.