In a large mixing bowl, combine the whole wheat flour, all-purpose flour, salt, and active dry yeast. Stir them together until they are evenly mixed.
Slowly pour in the room temperature water while mixing with a wooden spoon or spatula. Continue until no dry flour remains, and the mixture forms a shaggy dough.
Cover the bowl with plastic wrap or a damp towel. Allow the dough to rise at room temperature for 12-18 hours.
Once the dough has risen and is bubbly, lightly flour a clean surface and turn the dough onto it. With floured hands, gently shape the dough into a ball without kneading.
Place the shaped dough onto a piece of parchment paper and cover it with a towel. Let it rest for about 1-2 hours until it has puffed up.
About 30 minutes before baking, preheat your oven to 450°F (230°C). Place your Dutch oven inside to heat up as well.
Carefully remove the hot Dutch oven from the oven. Using the parchment paper, lift the dough and place it into the pot. Cover it with the lid and return it to the oven. Bake for 30 minutes covered, then remove the lid and bake for an additional 15-20 minutes until the loaf is golden brown.
Once baked, carefully remove the bread from the Dutch oven and place it on a cooling rack. Allow it to cool completely before slicing.