This if for, well, walking!
Walk 10 km total!
This is cumulative across all play throughs. Using the walk through, I didn't unlock this on my first play through. If you're needing a second play through you will no doubt get this in the process.
If not, you can simply load up the first chapter and walk around until it pops. Although it may be worth going into Chapter 2 and resting so you can get your gait to normal speed instead of limping in Chapter 1.