Hi! As far as I know, you should be able to... Download the castle_src_20180429_2310.zip package and see if it works for you. (Use %castle.rkt from the %src/ directory). That is the version that I compiled my submission from, so if they're not kidding about the cross platform-ability, you should be set. There are no dependencies outside of Dr. Racket.
Thanks for checking it out!