"a door to the room"
Translation:дверь в комнату
В + accusative indicates direction (into, towards) and в + prepositional indicates location (in, inside). Here комнату is the accusative case, so it's "to the room." If it the door was inside the room it would be в комнате.
A context-search at reverso.net returned a number of instances where that phrase is used to mean a variety of things, including "the door to the room", see:
«дверь в эту комнату» – не принято. Скажите, пожалуйста, разве это неправильный перевод?
Is there some particular reason you're asking a question is what may or may not be good Russian, in a course for English-speakers?
When use only Russian, you're denying yourself possible input from someone who can answer your question, but doesn't yet know enough Russian to understand fully what you're asking.
I usually ignore such questions, and certainly never try to answer them, even though I'm starting to accumulate a lot of information which has proven useful to others here. So, try English next time - you might actually get an answer to your question.
Your choice is fine. Report it when you will come across on this task next time.