Rinse them off under cool water to remove any dirt. Score the shells before you place them in a pan. Place the flat sides of the chestnuts down. Make sure that there's a bed of glowing coals that you can rest the pan on, whether you've lit a fireplace or a campfire. This should be enough to roast one side of the chestnuts. Lightly shake the pan around every minute or so to distribute the heat. After five minutes, use a potholder to remove the pan, roll over the nuts, and place them back on the fire.  Once you've roasted the nuts, wait 2-3 minutes for them to cool down and enjoy them while they're nice and hot.
Rinse the chestnuts. Score the shells. Put the nuts in a cast iron frying pan. Prepare the fire. Place the pan on the coals for 5 minutes. Turn the nuts over. Roast the nuts for another 5 minutes. Serve.