Hi Rhiannon
Nice piece about St Cuberts Well you have posted but it is refering to the Holywell..not the Victorian St Cuberts Well.
http://www.themodernantiquarian.com/site/6639/holywell.html
And yes you can squeeze into the upper chamber..
I like the way this has been given a disputed antiquity tag....it is possibly older than any other site on the website...
Mr H