Learn Danish: Hjorten løber ind i den mørke skov. - The deer runs into the dark forest.

Using ind i emphasizes movement from the outside to the inside, matching the English "into". If the sentence was Hjorten løber i den mørke skov, it would mean the deer is already inside the forest and running around in there.

Could I use inde i instead of ind i?

No, because inde is used for a fixed position (meaning "inside"), while ind implies movement or direction toward a destination. Since the deer is actively running into the forest, we need the directional ind.

Why does the adjective mørk have an -e at the end in den mørke skov?

When an adjective is used with a definite article like den or det, it must take the definite ending, which is almost always -e.

Wait, why is it den mørke skov and not den mørke skoven?

Unlike some other Scandinavian languages, Danish doesn't use a definite suffix on the noun when there is an adjective. When you use the standalone article den with an adjective, the noun drops its definite ending. So "the forest" is skoven, but "the dark forest" becomes den mørke skov.