dingit yes, it's on my list of places to go! I got a brochure for it this year but we ended up going to disneyland paris as we got such a ridiculously good deal we figured that would be a good one to cross off the list, particularly as ds2 is a huge mickey mouse fan and I can't see it lasting much longer especially with his big brother taking control of the tv remote and switching Mickey Mouse off. I also quite fancy trying the playmobil land in germany and de efterling (sp?). There's also Plopsyland in Belgium which sounds so bad it's tempting to drag the dc there just so we can laugh about it later.
If you look at the michelin site, you can type in destinations across Europe and it will give you directions as well as estimates for the amount of fuel (and thus cost!) needed, which is a fun way of wasting time doing valuable research before deciding on a destination.
Before we had the dc we did a fair bit of cruising. Took me years to persuade dh to try, eventually he gave in and then he loved it. We loved the not flying, exploring lots of different places without the need to pack and unpack all the time, the opportunity to just chill out and relax, and the general ease of the holiday. I think the dc are just about getting to an age where they would like it too but I think that you have to book quite early to get a decent family cabin which can be much more expensive - we were in a position to book late and grab great deals. There's something very nice sitting on a comfortable lounger reading a great trashy novel, watching the coast of north africa peel past you, the bar lady coming out every 20 minutes to see if you want any more drinks or nibbles, beautifully warm but out of the direct sun, another couple of people sitting on loungers on the other side of the door that by the end of the fortnight you know well enough to nod to, the odd person doing a round the deck walk going past but otherwise being undisturbed... bliss! But probably not going to happen with young dc, I know 
Places we've stopped off en route on a cruise or on general travels that would be great to go back to with kids include the north german coast - warnemunde and rostock, travemunde and Lubeck, Tallin in Estonia, Copenhagen, Helsinki (ok some of these are getting quite a way away!), southern french coast around nice and eze, perpignan, avignon and Bilbao/Sans Sebastian.
We did a north african cruise for our honeymoon and trained down overnight to Cadiz via madrid, caught the ship, did the cruise and ended up in Athens. Then spent a few days there, got a ferry over to Italy, train up to Bologna for a few days, then another train to paris and on to home - the journey became a fab part of the holiday and was very easy, especially when you break it all up.
Bizarrely a cruise can be a very outdoorsy holiday - when you get to a destination you are out exploring it, depending on where you go there are often beach days or adventure walks as well as just exploring the big tourist destination you are near to do. And then when you have a sea day, there's the swimming pools - but many of the big ships now have things like climbing walls, ice skating, surf pools, crazy golf and more. ANd then lots of them offer babysitting in the evening - there are usually kids clubs on board that at night you can drop them off and they have it all quiet and snoozy, maybe a gentle dvd playing in the background, and lots of mats and blankets for them to snuggle up and go to sleep. Then you pick them up at 11 or midnight or whatever you've agreed. Means that you don't have to worry about them being alone in the cabin while you are eating or dancing or watching the shows or just enjoying a quiet moment for two, nor do you have to go to bed when they need to either! Not something you'd want to do every night, but nice to have the option. And obviously the whole place is fully staffed with the child care staff that - for boats sailing from the uk at least - tend to be crb checked and all organised very professionally. Some cruises have themes - first one we went on had a footie theme, a couple of big name but probably slightly past it players and coaches that ran sessions for the kids during sea days and some 'tell it as it is' talks for the grown ups. Before my time of having kids, plus I hate footie so didn't bother with it, but the kids seemed to love it and I can imagine ds1 loving it now, although not ds2.
oops sorry - just realised this turned into a bit of a mega epic post 
got a bit carried away on the memories!