It's as easy as blocking out some time, hopping in your car, and going for a drive with no destination in mind. Or getting on the train and getting off at a new stop.
Stop when you see something intriguing, eat something you have never tried before, take back roads and side streets, and have a conversation with a local.
Don't forget your journal/sketchbook so you document your adventure.
This is my favorite thing to do when I need to recharge my creative batteries, I have gotten some of my best ideas while in the car. Plus I have found some pretty amazing places that have become my favorite places to go.
When was the last time you had an unplanned adventure?