"If You Could Read My Mind love,what a tale my thoughts could tell." "Just like an old time movie,'bout a ghost from a wishing well." In essence he is saying that his "love" would find his thoughts either entertaining or attention grabbing,like a good movie,or in this case,the kind of movie that he mentions in the song. When he says,"In a castle dark or a fortress stong,with chains upon my feet", he means that he would rather keep his thoughts locked up or to himself. Hope that helps!
Borderstone,outta here and Alberta Bound!