I would suggest going online and looking through
gobo catalogues and finding the
gobo that you want, then calling a company (I personally use
production advantage, google them) and ordering the
gobo that you want. Then its the simple matter of putting it in the light, and focusing said light.
Rosco has some nice gobos, plus their catalogue is online
here
Gam also has some nice gobos, but I don't think their catalogue is online.
There are thousands of other companies that make and sell gobos, if you do a quick google search you will find several companies.
You could also make your own artwork and
send it to several companies and they will cut you gobos from that artwork, so if you have an artistic
image of the castle, you can have them cut that
image.
You really can't just come here and post the question "i want a castle, tell me what to get", art doesn't really work like that. I hope the
Rosco gobo catalogue gives you a good start of what your looking for.