This isn't Sheffield so I apologise, but this seems like the right section to use.

Yesterday I was in Stand Woods behind Chatsworth house and for the first time noticed a huge stone monument (very much like an obelisk) tucked away amongst the trees. There's no inscription on it from what we could see, but there was a tunnel leading under it which, in the other direction, seemed to lead through a wall and into the formal gardens. I couldn't find anything about it on the Chatsworth website, but maybe I just missed it.

Does anyone know which monument I mean? If so, has anyone any idea what this monument was built for, or if it serves any kind of purpose?

Thanks!