Not sure!

Had a geocaching walk around Houghton Green Pool (Warrington) with friends today, grabbing mostly puzzle caches which we recently solved. We spotted this structure on our walk and we think it may be some sort of ventilation shaft for the tunnels of the former Parkside Colliery, which run underneath.
The sun was out today and it was cold. Great walking weather. It had rained heavily last night and through the night though so there was a lot of mud and some waterlogged areas.
The pool has shrunk to a fraction of the size it was less than 10 years ago - it looks like it may disappear entirely.
We found all the geocaches. 
Still no lateral flow tests available!