We visited this castle - in Brussels itself - quite by accident. We got turned around driving in Brussesls (have I mentioned the sign issue?), and ran across a castle in the middle of a small park. There was an open parking spot, so we scooted in. There's a small museum there, but it was closed - we had used up that part of the day elsewhere. Here's the history behind the castle:

And here's a view of the castle from a few steps back: