Walking, running, standing, or sitting barefoot, will ground you.
Outside: grass, soil, gravel, stone, sand, brick, concrete. Inside: unpainted or unsealed concrete or tile floor built directly on the Earth (best to test the floor for conductivity). The following surfaces will not ground you. Outside: asphalt, vinyl, wood (such as wooden decks). Inside: wooden floors, painted/sealed concrete or tiled floors, carpets.

A human body – our brain, heart beat, our muscles, everything – is pimarily electrical.  So when we’re standing barefoot on the earth, we’re absorbing electrons that help neutralise the free radicals in our body that damage our cells.  We feel better because we are electrically stable.