To describe the physical terrain you are traveling through or along, Russian often uses the bare Instrumental case. You can express "through the forest" or "by the trail" without using any prepositions at all—just put the noun describing the terrain into the Instrumental.
The Bare Instrumental of Route
This structure is commonly used with verbs of motion like идти (to walk/go).
| Do you want to go through the taiga or through the swamp? | Вы хотите идти тайгой или болотом? |
If you add adjectives or pronouns to describe the route, they must also take the Instrumental case to match the noun.
| The guide said to walk by this narrow trail. | Проводник сказал идти этой узкой тропой. |
| There is no way for us to pass through this impassable swamp! | Нам не пройти этим непроходимым болотом! |
Making Your Way Through the Wild
This case is frequently used with verbs that describe a struggle, such as пробираться (to make one's way) or плутать (to wander). Notice how plural nouns like заросли (thickets) take the plural Instrumental ending (-ями).
| We were slowly making our way through the dense thickets. | Мы медленно пробирались густыми зарослями. |
| We need to make our way through the dark forest, and then walk along the forest edge. | Нам нужно пробраться тёмным лесом, а затем идти опушкой. |
Ridges and Shores
You can use the bare Instrumental of route for almost any continuous geographical feature you travel along, from a forest edge (опушка) or a shore (берег) to a mountain ridge (хребет).
| At night we decided to walk along the shore. | Ночью мы решили идти берегом. |
| The guide is carefully making his way along the ridge. | Проводник осторожно пробирается хребтом. |
