Parent category that leads to a list of the parents sub categories

I am building an art website for a friend.

http://www.mariocastillo.net/gallery/

I want all listings of the parents categories on the right (which I have figured out) However, when they click on “Chupicuaro” I want the sub categories thumbnails to be listed on that page. Basically, there are sub categories under Chupicuaro that I want to group in one page as thumbnails.