Learn Polish: Jak możemy dojechać do zamku? - How can we drive to the castle?

Jechać just describes the continuous action of driving or riding. By adding the prefix do-, we create dojechać, a perfective verb that specifically means to successfully reach a destination by vehicle. Because we are asking how to get all the way to the castle, we need this prefixed version.

Why is do repeated, first in the verb dojechać and then as a separate word?

This is a very common pattern in Polish! When a motion verb uses a prefix to show a specific direction (like do- for reaching a goal), it is almost always paired with the matching preposition (the separate word do, meaning to). Together, dojechać do means to drive to or reach by driving.

Why is the word for castle spelled zamku instead of zamek?

The preposition do always forces the noun that follows it into the Genitive case. For the masculine inanimate noun zamek, the Genitive ending is -u, making it zamku. Notice that the last e drops out, which is a very common vowel change in Polish nouns when adding endings.

Where is the word for we in this sentence?

The pronoun my (we) is dropped because the verb możemy already has the -my ending, which tells us exactly who is doing the action. In Polish, it is standard to leave out subject pronouns unless you need to emphasize them.