I'm sure there are packages geared to this sort of holidat but for absolute romance coupled with the experience of a lifetime why not try Borneo It's easily the most romantic and amazing place I've visited in many years of serious travel Take a boatride at dusk to watch the wildlife otters fireflies incredible birds going home to roost etc just wonderful the orang-utans mustn't be missed either and the beaches around Damai Beach are wonderful.Another idea is Sri Lanka thats romantic too b ut Borneo beats all even the best Caribbean islands as it's so un-touristy as yet and the people are so welcoming
My sister is off on an eastern Med cruise for her anniversay in September. You can arrange for champagne & flowers, as a suprise for the other half ,in the cabin.
I don't know what sort of destination you're looking for, but for our 25th we went to Copenhagen and got incredible treatment at the Palace Hotel. We hadn't booked anything special, but our travel agent had told them it was our 25th and we were upgraded to a luxury suite overlooking the main square, champagne (not just any old fizz - the real deal) and a complimentary 5-course dinner.