Lol wow..
Hmm well the easiest thing to do would be to pick song lyrics you know.. something like 'Lucy in the Sky With Diamonds' is an awesome imaginative journey!
And if you know your art and how to analyse it, choose an artwork as they're pretty easy to write about. Surrealism and other abstract art is great.
Otherwise, I'm assuming at least some movie you've seen has an imaginative element to it, haha
Even if it's not a big component to the movie as long as there's something there should be plenty you can write about it!
Good luck