Last year, we held a "Cruise" themed party for my daughter's 10th birthday.  Because her birthday is in December, we are limited mainly to indoor activities, and she really wanted to do something involving a sleepover and swimming.  So, we came up with this theme, and rented two rooms at a local Embassy Suites (enough room to accommodate about 10 kids total).  Upon "embarkment" when the parents dropped off the kids, we met them in the hotel lobby and presented them with a lay and took their pictures.  We decorated the rooms with a cruise ship and tropical island look. We printed up a "Ships Itinerary" for each girl with all the planned events.  After a swim in the indoor pool, they returned to the room (AKA, the ship's main dining room for a pizza feast). This was followed by a series of games and contests with play money being awarded to the top 3 contestants.  At 11 PM, the girls got to bid on a variety of prizes (different that the standard gift bag idea). This was followed by a "mid-night" buffet of snacks.  The next day, after breakfast and another swim, the kids "disembarked".  According to my daughter, this was the best Birthday Party idea any of her friends had ever seen!