You have to walk through the 5 'backtracker' gates found on footpaths. You don't have to move far or stay long (for me it was only a couple of meters and until the time-shift fiished). These gates are locked by default and they only unlock when you reach the other end.
Although this seems easy, the achievement is glitched and not always unlocks when it supposed to (for example it definitely doesn't work if you try it after opening the bunker).
Therefore it's recommended to do this in a separate playthrough ('running all the way to Little Tipworth and back through the gates), in which case it WILL unlock. Alternatively, you can try to do this right after unlocking Radio Enthusiast.

Past the tractor and the ringing phone there's a small gate which leads to the bigger backtrack gate. You'll come out over a lookout map next to the northern field.

From Little Tipworth:


From the Appleton Farm:

There's a hole on the western fence:


From Appleton Farm:


From Tipworth Forest:

On the southern side of the lake there's a footpath which takes you to an area I'll call 'Hub' with an event at an intersection:


If you take a right there, you'll come across a bench with a grey radio. The path will fork again soon, you should take a right and you'll find yourself just below the building with the treehouse.

From the hub:


From Tipworth Forest:

From the same hub, after the grey radio take the left path. You'll come out at Haverton Road at the beginning of Tipworth Forest.

From the hub:


From Tipworth Forest:

If you follow the left path from the event mentioned above, you'll come out at th back garden of the house with the canopy swing, very close to the Yaughton sign.

From the hub:


After emerging from the bushes:


From Yaughton: