Lundy Island. Car free. Boat from North Devon. Accommodation booked through landmark trust. Eat at the tavern on the island...you are a captive audience but prices for once are sensible. Or you can self cater.

Scilly Isles. Boat, or plane or helicopter. Accommodation from camping to very expensive hotel (and everythign in between). Stay on St Marys and travel to out islands each day, or stay on one of the out islands. A hidden treasure.

Trip on a manned canal boat - i.e the hosts steer you and cook for you - it is quite expensive but something my family will try in the future

I know this is not available all year round - so you will have to check

One thing I've always fancied a go at is the Llama Expeditions run in several places around the South Coast, several venues in Sussex, Ashdown Forest etc offer them - certainly would be different.

If you have an older family, had you considered a working short-break for the National Trust - can get stuck into pond-clearing, dry-stone walling etc etc ? http://www.nationaltrust.org.uk/main/w-trust/w-volunteering/w-workingholidays-list.htm?regionID=&month=10&year=2006&holidaytypeID=K&searchstring=