Time to work your brain! Are you Sensing in your approach to learning? Time to read a little poetry. Intuitive? Find yourself a nice thick textbook and give it a read!
Intuitive people like to take in information and process it, looking for patterns. So reading a factual book might be frustrating or boring. Still, it is important to be able to read and follow directions, so this is a great stretching exercise.
Sensing people are very fact oriented. Poetry is all about metaphor and layers of meaning. So taking some time to read poetry allows you to stretch your normal methods of data processing.