In reply to Matt Vigg:
Yeah, bareboat means you sail it yourself. It's the same deal as car hire, but you do have to have at least one person on board with relevant sailing qualifications.
IIRC, last time we went in 2011 the cost pp for flight and share of charter was about £600 for the fortnight and there were 6 of us on a 38ft boat. Food and fuel not included. A number of resorts offer weekly sea kayak hire, Vassiliki on Lefkada is one that I know of.
If you're limited to being land-based there's great potential for bouldering on Kefalonia about 5kms from Sami on the road to Poros up on the left. DWS north of Fiskardo along the coast footpath and near Afales on the Lixouri Peninsula. Paliokastritsa on Corfu is a picturesque resort with extensive crags on each side of the bay and the west coast of Lefkada is impressive.