Please unlock the discussion!
Clearly, there are problems with the forum, however, if the discussion is locked there is no chance that somebody will ever answer my question, is it?
That is weird - there is a German discussion inside a sentence that's marked as being part of the French course. It's probably locked until they can get that bug sorted out.
In the meantime, feel free to ask your question in the German (or French) discussion forum!
Having looked at the bugged page linked to, I entered the German forum and searched for "Er fährt zu einem Schloss."
On the page which came up scottaumont had written the following:
'nach' - for place names and directions
'zu' - everything else
Hopefully that's of some use to you - either the quote or the link to the page itself. :)