Learn Dutch: Waar moeten we heen? Rechtdoor! - Where do we have to go? Straight ahead!

Waar ... heen means "where ... to". In Dutch questions, it is very common to split them up. The question word Waar goes at the beginning, and the direction word heen goes at the end of the clause.

I see moeten (have to), but where is the verb for "go"?

It is hidden! In Dutch, when you use a modal verb like moeten (must / have to) or willen (want to) along with a clear direction word like heen, you can leave out the actual verb of motion (gaan). Saying Waar moeten we heen gaan? is also correct, but dropping gaan is much more common in everyday speech.

Could I use naartoe instead of heen in this sentence?

Yes, absolutely! Waar moeten we naartoe? means exactly the same thing as Waar moeten we heen?. Both are frequently used to ask "Where to?".

Is rechtdoor related to the word door (through)?

Yes! Rechtdoor is made up of recht (straight) and door (which often means "through" or "onward" in Dutch). Literally it is like saying "straight onward", which gives us "straight ahead".