My husband and I are members of the Church of Jesus Christ of Latter-day Saints. As part of our religion we believe that families can be sealed together for all eternity. These sealings take place inside of temples all around the world. Many people who are not members of our church think that these temples look like castles, which gave Seth the idea to mash them up with another castle.
This temple is in Rexburg, Idaho, although there are a few temples around the world that use a similar design. You can learn more about it and this design here.