If you are planning to visit Berlin, well take a train and visit also Sanssouci!
It could be expensive if you want to see the palace inside, but if you are used to very well guided tours, well... forget it. It's a quick showing of some rooms, worthy only if you want to see the famous paint of Fritz as adult.. of course, if it's not in restauration (thing that happened when I visited it).
The gardens are beautiful and huge, and you can visit them just giving an offer (suggested offer was 3-5 €, but it's worthy!). Don't forget to admire the vineyards in front of the palace (they were a revolution at Friederich I 's time), and take a long quite walk all around.
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