Peel Street Caves

'[Image: A 3D laser scan of the Peel Street Caves—actually a former sand mine beneath the city—courtesy of the Nottingham Caves Survey].
It's hard to resist a note that says a "new cave" has been "uploaded," but the Nottingham Caves Survey—previously mentioned here—has announced just that, putting 3D laser scans of the incredible Peel Street Caves on their website.
Like smoke rings breaking apart and slowly looping inside the planet, their near-endless recursivity makes it almost impossible to see where they begin.'
http://bldgblog.blogspot.com/2011/01/peel-street-caves.html