What do you think about castles in the air? Is it fruitless to dream about things that either may not happen or can not happen? I personally don't think we would create them if we didn't feel a small sense of hope that they were at least . . . possible.
Castles in the air can be built in reality. Not all of them certainly, but if we take the first steps toward at least one of them, we can build a foundation for our castle. It could be we are looking for a new job situation, or we would like to see ourselves living somewhere else, or we would like to become better at a certain talent or hobby that is important to us. Whatever it may be, I don't think that we should envision our lives without castles in the air.
These castles give us somewhere to go. If we've had a hard day, it's nice to have a "happy place." Maybe you see yourself at your favorite vacation place or picture yourself settled with a family and growing old with someone. It gives you something to build for, to plan for, to hope for, and when you've actually reached that place you've prepared for, you have accomplished something truly wonderful. You'll look back on your life and be satisfied.
On the spiritual side of things, we should envision our castles in the air in relation to eternity. St Teresa of Avila said, "I thought of the soul as resembling a castle, formed of a single diamond or a very transparent crystal, and containing many rooms, just as in Heaven there are many mansions." We should be building for our home in Heaven through virtue, prayer, and good works, which will make our soul beautiful and reflective of God's presence like a diamond reflects light.