Minecraft wiki entry for Building_a_metropolis, associated text: Cobble/Stone brick path:
Recommended material: Cobblestone or stone bricks.
Should wind around anything that requires more than a small amount of pickaxing to destroy. These generally should not be connected to any large long bridges, only small stone or wood ones with no extra support needed.
Should be 2 to 3 blocks wide.
Can be any reasonably walk-able steepness (up to 1/2 slope).