French language Q&A Forum

I was doing the exercise (https://progress.lawlessfrench.com/my-languages/french/exercises/judge/1833/14548249?response=4150265&page=7) to answer a question and now have one of my own:

There's the phrase: visiter les ruines du vieux château.

How come the rule that the definite article is omitted if there's an adjective intervening between de and the noun is not applicable here? I would have thought this should be ...de vieux château.

Not really a French question, but how do you type a dash to get a "your answer matched mine" in the writing exercises? Even if I write exactly the same as the model answer, if the phrase begins with a dash the computer doesn't credit me with getting it right. Is it something to do with the number of spaces before or after? Or is there a type of dash I'm not using? 

Frustrating as I challenge myself to get 3 or 4 "matches" per exercise, but this means half of my attempts have no chance....