Well, according to their site - http://www.caer.co.uk/fogou.htm - there's no mention of not being open or owt... Here's the contact details:

Founder-Director: Jo May BSc (Hons). Dip IDHP. Dip CPP. AAPP. UKCP

CAER,
Rosemerryn, Lamorna, Penzance,
Cornwall, TR19 6BN, UK.
Tel: ##44 (0)1736 810530
www.caer.co.uk
[email protected]

(Obviously just cut and paste from the site - hope that's OK!) Give em a call! Take loads of pics cos I've always wanted to go there!

Have fun!

(Jealous) G x