Thank you Chani, for the endorsement, though other responders have a wealth of experience (particularly the Brits, who are so lucky to be much closer to Greece for more frequent and less costly visits!). My forte is practicality -- finding beautiful places in Greece isn't hard, what's more important is avoiding pitfalls that can mar your experience. And for that, Nigels we need lots more Facts; For instance:
• WHEN would you llike to go? advice much different for hot crowded High Season (july-August) vs late May or Early September.
• HOW LONG would you have? 2 weeks? 3? If you have less than 12 days IN greece, not really advised.
• Nature/extent of wife's disabilty (Important). Does she need to use wheelchair or mobility scooter most of time? Or can she walk but for limited distances, such as 100 yards? Can she do ANY stairs or must she always be on street -level lodgings or bldgs w elevators? Also, does this affect stamina, i.e., is daytime activity limited to 3-4 hours, plus nap (usually if age-related).
• Desired experience/activities? Any beach time, sitting or in water? Is main interest natural beauty, some historic/classicl interests?
As others have touched on , this would affect cruise choices greatly! Those huge mega-cruisers are not for you.. thousands of people crowding, pushing rushing. Ships parked offshore with "tenders" taking you to docks jampacked busses etc. Lin's rave for a Danube cruise was not germane -- small boats on a river, step easily right onto pavement. Even the smallest (and more upscale) cruises would involve several hundred, and deailing with gangplanks to a dock. And the pace of travel for the larger cruises (arrive in morning -- 7-8 hours max on island, back on board before sunset) does not really provide the Greece experience you want.
However, a compromise IS available -- a Greece "tour" that YOU design (with help), and a skilled Greek agency makes all arrangements -- transportation, lodgings, local day-tours, car rentals when desired, etc. If Nigel will share their situation & interests more specifically, I think we "forum-ites" can help him choose a very scenic and feasible itinerary, and there are several well-regarded Athens-based agencies who do a fine job when given facts/interests & budget. This could end up costling less than a cruise, with better experience. A lot of us will enjoy helping Nigel work on this.
As a start, with practicalities -- TIMING -- i think its best to try for 2027.. and in my experience of 13 extended trips, I think the ideal time to go is Mid-May.... and the 2nd option, early to mid-September. As for classic ruins/ landmarks -- I think Delphi would be Very Difficult ... but other famous & fascinating ancient ruins/landmarks are easier to access AND enjoy... in a few days, driving easily on excellent roads and low-traffic byways only a few hours from Athens. And you can have a wonderful "mini-cruise" experience in a daytrip right from Athens, if you choose the right ferry, to the right nearby island.
I hope Nigel will respond with more information, so we can share what we've learned (it's "travel-therapy" for those of us who are not going to Greece this year)