Learn German: Wir fahren nach Westen.

Even though you are learning two-way prepositions for direction (like in or auf), compass directions (North, South, East, West) typically use the fixed preposition nach to mean 'towards'. Remember that nach is always a dative preposition, not a two-way preposition!

Could I use a two-way preposition like 'in' here instead?

Yes! You could say Wir fahren in den Westen. Because in is a two-way preposition and you are showing movement toward a destination, it takes the accusative case (den Westen). However, in den Westen implies driving into a specific western region, whereas nach Westen simply means heading in a westerly direction.

Since Westen is a noun, why is there no article after nach?

Compass directions are masculine (like der Westen). But just like when you travel to most cities or countries (e.g., nach Berlin), when you use nach to show direction toward a point on the compass, you drop the article completely.

If the translation is 'driving', can this sentence also mean we are taking a train west?

Exactly. fahren means traveling by any kind of vehicle (car, train, bus, bike). While English often uses 'going' for these, German requires fahren anytime you are using a vehicle, reserving gehen strictly for walking on foot.