The Natural Stone Path is a building-block looking like flat stepping-stones on moss on one side and like a natural Grass-block on 4 sides, while the underside looks like Dirt. It can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015), but only after the crafting-recipe has been unlocked upon taking/crafting a Stacked Stone Wall for the first time (which in turn is unlocked when taking/mining Stone for the first time. To craft 8 (blocks of) Natural Stone Paths, you'll need (as of R27 in January 2016):