Try the positioning cruise on Splendour of the Seas to the Med we went on her in April 2000 = Miami to Barcelona and the 6 days at sea shared with our fantastic table mates were brilliant! You can do nothing, dink, eat, sleep, drink again, read a book, swim, run, swim, drink again....the list is endless. Royal Caribbean takes some beating for entertainment at sea.
Go on an Anniversary cruise. You will get loads of extras if you do. P.& O. do them.
Enjoy your celebrations. Coli.