We visited Benrath during the morning. We went there by metro. Takes a while though. But the metro stop is right before the entrence. You can also take the train to Benrath station. You need to walk to the castle for about 5-10 minutes.
Unfortunately the 2 museums and the castle were closed when we arrived. But you can walk around the castle and visit the gardens for free.
Don't forget to bring a visit to the small town Benrath. Nice little shops and churches.
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