Yesterday I ran 7.5 km. I know it might not be big on the marathon scale but if felt bloody amazing. This distance possibly is more than I ran in my life before. Total. Combined. And yet I was able to pull it off and honestly - felt quite great once I finished. Interestingly I did not plan on doing it, but I like "exploratory" running so much I just got carried away.
The principle is quite an easy one. Just get out there and see what's behind the corner. And behind the next one too. And carry on as long as you feel it's fun. There are only two recommendations I would make: try to run in a big circle, so you are close to home at the end or accept the fact that you'll need to run back in the end. That's what happened to me - wanted to run 3 km, but at the end of the three I was in the middle of nowhere and had to get home. So I ran back.
You might wonder why 7.5 km rather than six? Well, that's where the 2nd recommendation comes in. Carry a smartphone with full battery to handle GPS mode. Or you'll run randomly trying to find your way back and you'll cover some extra mileage. Don't get me wrong - it's still fun but you've got to have time for this so the best time to go a bit ga-ga with your running might be the weekend.