In a large bowl, whisk together the flour, salt, and yeast.
Add the cranberries and walnuts; toss to combine.
Stir in the warm water, adding a little bit more (if necessary) to bring the dough together just until you can't see any dry pockets of flour.
Cover the bowl and leave to rise at room temperature for about 18 hours, until the dough has doubled in size. It will spread out in the bowl and look bubbly.
Place a piece of parchment paper on the counter and dust with flour. Gently nudge the dough from the bowl onto the parchment. Shape the dough into a loose ball by gently folding under the edges.
Cover the dough with plastic wrap or a towel. Let the dough rest and continue rising for about 30-60 more minutes.
While the dough rests, place a 4-6-quart cast iron Dutch oven (with the lid on) in the cold oven. Preheat the oven to 475°F.
Once the dough has rested for 30-60 minutes, carefully remove the hot pot from the oven. Take off the lid. Pick up the parchment paper and gently place the parchment paper (with the dough on it) into the pot.
Cover the pot and put it back in the oven to bake for 30 minutes.
After 30 minutes, remove the lid and continue baking for an additional 10-15 minutes (or until the loaf has turned a deep brown color).
Allow the bread to cool on a rack for at least 1 hour before slicing and serving.