A summer party is always better with a bouncy castle in the mix, it just is, and that's a rule. A lot of people unfortunately get the idea that a bouncy castle is just that, a castle, but it's not true, the term bouncy castle is generic for an inflatable piece of fun that can be anything from a pirate ship, a huge transformer that the kids can climb all over, a slide complex to yes, a castle or a cage for actual bouncing. These inflatable's and their variety can give you all manner of ideas for a party theme, or do it the other way around, decide on a theme, then go to the party supplies store and pick out your bouncy castle to accommodate your idea. I like the one that is a boxing ring inflatable, it has a bouncy floor and inflatable "ropes" to keep in the participants; you get huge inflatable "boxing gloves" or those sumo suites and go for it. This venue is fun for everyone, the little kids can use it for simply bouncing and the older guests can stage sumo contests until everyone is so worn out, at which point they will just want to sit down and relax. There is a bouncy inflatable for that too. You can get a nice Hawaiian beach with palm trees and lounge chairs and sand, a whole scene just for relaxation.
If you want a castle, there are many to choose from, you can have a Disney castle or a princess castle, or for the boys, a castle designed to be defended against the Mongol hoards, accessories for this include inflatable swords, and while you are at it, a pirate Bouncy Castle is another fun way for the kids to spend the afternoon at the party. Stop by your local party shop for eye patches, pirate sashes and bandanas.