Feel like adding a bit of a kick to your run?  Try Fartlek training.
Fartlek (pronounced fart-lick), meaning ‘speed play‘ in Swedish, can be as much fun to do as it is to say.
I have seen some planned fartlek workouts (ex. run 3 x 3 min hard)- but I just call that interval training.  To me, farleks are unplanned speed bursts.
Pick a landmark (ex. the next bench, the 3K marker on the trail, the third telephone pole) a run hard until you reach it.  Slow down and recover, then pick your next landmark.  Some stretches will be longer (a few minutes) and some will be shorter (20 seconds or less).  Then randomness of the workout is what makes it fun.  If you are running with a partner, take turns picking the next landmark.
Not all runs have to be planned and purposeful.  We are athletes, training for the sport of life.  A random, sort-of fun, workout is great training!
Enjoy your run!
–Tanja