Sometimes it is fun to spend your weekend doing the same things you enjoy, but after a while this can get boring. While sometimes risky, adding spontaneity to your weekend is as simple as changing your location without knowing beforehand. Rather than staying in your city of residence, visit the nearest train / bus station (or even airport), and find the cheapest flight in a certain direction. Even if it is just for the weekend you’ll find plenty of fun things to do.
More importantly, you’ll be less inclined to create a plan that restricts your freedom while on vacation. While living in Europe, I often took the cheapest bus possible and ended up spending one entire weekend in Lviv, Ukraine with automobile smugglers and openly corrupt politicians. Now that is how you add spice to your life.