I think that any subject can be made fun. It's really more the methods of instruction or learning that are the key to fun.
And variety is important. What is fun will cease to be fun if it is done daily. So varying your methods will increase the "fun factor." Games one day, hands-on projects the next, a field trip after that. Reading a fantastic living book, watching a documentary, making a craft, acting out a story, The list goes on and on.