The cone's eye in Catcliffe

This glassworks building - or 'glass cone' -  dates back to 1740, and is the oldest surviving structure of its kind in Western Europe.  It's located on the south-eastern edge of Sheffield, now surrounded by modern houses.  At twenty metres high, it dominates its surroundings.
The Cone narrowly escaped demolition in the early 1960s, when I think the local council was on a postwar modernising and building mission. Local campaigners were able to rescue it, and eventually to ensure its protection and maintenance. It's now a Grade 1 listed building.  There's more info here:

https://en.wikipedia.org/wiki/Catcliffe_Glass_Cone

The main shows the somewhat dizzying view from inside, looking straight upwards. To me it looks a bit like a cyclops eye. The extra has a more informative view of the whole building.