The Best Method: Dampen the Loaf and Bake it
Without a doubt, the best way to revive stale bread is to dampen it and pop it in the oven. Preheat your oven to 375°F. Grab a spray bottle and lightly spritz your bread or wet your fingertips and pop the bread onto the middle rack. Bake it for 7 to 10 minutes. When you take it out, you should have lovely soft on the inside, crusty on the outside bread you can enjoy again.
Go the Extra Mile: Wrap Your Bread in Foil and Bake it
Are you sensing a trend here? Reheating your bread in the oven yields the best results for reviving a stale loaf. If you're not in a rush, dampen your bread, wrap it in foil, then bake it in the oven at 300°F for 30 minutes, plus another 5 to get the crust nice and crispy. It takes a little longer but will get you the closest result to a freshly baked loaf.
Works in a Pinch: Microwave Your Loaf
Now microwaving your bread doesn't yield as tasty results as the other two methods, but if you don't feel like turning on the oven or are looking for the fastest way to reheat your bread, the microwave is your best option. Lightly dampen a paper towel and wrap it around the bread. Microwave the bread at 10-second intervals until it's soft. Don't overdo it with the microwave times because it can make the crust soggy.
Keep in mind that whichever method you choose to revive your stale bread, the effects are short-term. You'll need to serve and eat the loaf within a few hours.