The other St Cubert's Well in the holiday park may have been rebuilt (that recently added cross on top is hideous) but I wouldn't dismiss it as some sort of Victorian folly. The main structure of the well building is reputed to be 14thC, see for example, Cheryl Straffon's "Fentynnyow Kernow", or J Meyrick's "Holly Wells". It was roofless and largely ruined when visited by Charles Henderson in 1924, and one door jamb was being used as a pig trough at Trevornick Farm. It was restored by the Newquay Old Cornwall Society - hence the Cornish inscription. (See also "the Healing Wells and Cornish Cults and Customs" by PO and DV Leggat.) This well is genuinely an ancient holy well and both have a long and well established link to St Cubert.

BTW not only is it possible to squeeze into the top chamber of the well in the cave, but you can get several good friends in there together - good friends because it's a tight squeeze.

I'm sure you've seen this - maybe it's where you got started from. I'll keep an eye out anyway. Bellarmine looks like one of those tricky names that could be spelt any of 100 ways.
http://www.british-history.ac.uk/report.aspx?compid=50857