Located on the south-western border of Berlin and the capital of the state of Brandenburg, Potsdam is well known for being possibly the most beautiful city in all of Germany. Once home to Prussian Royalty and therefore full of historical palaces and stunning gardens, the city is almost entirely world heritage listed and makes for a truly stunning day trip. Before leaving Berlin, it might be an idea to pack a nice picnic, as the area is full of beautiful parkland and gardens and if the sun is shining, there is nothing better than finding a nice spot to sit and eat amongst the lush greenery.
Getting there is easy, simply hop on either the S-Bahn (S7) or RegionalExpress (depending where in Berlin you're travelling from). Using the S-Bahn if you have a ticket valid for A,B and C zones you're covered for the trip to Potsdam, you just get off the train at Potsdam Hauptbahnof which is the most central major station. The trip should take just under 45 minutes from a central Berlin station such as Friedrichstrasse and roughly 1/3 less time if you take the Regionalexpress which has slightly fewer stops.
There are plenty of things to see and do in Potsdam and it is highly recommended that you take a guided tour of the city, either by boat or by foot, for a great wealth of knowledge on the history and stories behind some of the city's most beautiful attractions. However the following are a few of the 'must-see' sites that the city has to offer:
Hollandisches Viertel (The Dutch Quarter):
A novel sight to see in Germany, the Dutch quarter is an area of roughly 4 blocks, filled with houses built in the typical Dutch style. With exposed red brick exteriors and shuttered windows, the buildings (built between 1734-1742 by Dutch craftsmen) are dotted with lovely cafes, boutiques and restaurants as well as a couple of small museums dedicated to the quarter and its architectural design. 
Holländisches Viertel — Photo courtesy of François Philipp
Schloss Sanssouci (the Sanssouci palace):
This stunning palace was once the summer residence of Frederick the Great and is known as being the best example of Rococo architecture in all of Germany. The palace was constructed by Georg Wenzeslaus von Knobelsdorff according to the design sketches made up by the King himself. There is a gallery on the premises which houses fine artworks by artists like Panini and Watteau. Guided tours cost just 8 euro and provide fantastic insights into the palace history. While you're there, take a long stroll through the stunning Sanssouci Gardens and find yourself the perfect picnic spot!
Schloss Sanssouci — Photo courtesy of Nigel's Europe
Down Town:
Take a walk Down Town for the full variety of the city's most picturesque buildings and sites! From the Old Town to New Town, you'll stumble across beautiful churches like the French Church (looks much like the Roman Pantheon) and the Parish Church of St. Peter and Paul. Situated quite close to the Dutch Quarter you'll find the Nauen Gate, one of Potsdams oldest buildings. The New Market is one of the most attractive surviving Baroque squares in all of Europe and The Brandenburg Gate (not the same as the Berlin's Brandenburger Tor) sitting at the western end of Brandenburg Road is also definitely worth checking out (even if only for comparative purposes). [PHOTO_201434]
However you go about spending your time there and no matter what sites you fit into your day, Potsdam is a truly magnificent and historically rich city, well worth the short trip from Berlin.