Berlin is your portal to the adventures of northeastern Germany and the surrounding states of Brandenburg, Saxony, Saxony-Anholt, and Mecklenburg-Western Pomerania, while a cross-over into Poland is quite easy by train. There are numerous nature areas within an hour or two of the city, while a touch further away you'll hit the coast of the Baltic Sea and the resort islands that make traveling here so enticing.
If you're looking to stay in the cozy confines of Berlin, you'll have plenty to keep you busy. First off, you'll want a way to see the sights. Despite the fact that Berlin is quite spread out, many of the sights worth your time are within biking range. So rent a bike; it's much cheaper and more autonomous than other forms of transport. As for the sights, the Berlin Zoo, which is on the edge of the impressive Tiergarden in West Berlin, has the widest range of animals on Earth and also has an excellent aquarium. The Tiergarden itself is huge and central, making it a great place for escape or for visiting the high concentration of cultural establishments in its vicinity. In East Berlin, the Tierpark is another quality zoo on the former grounds of Friedrichsfelde Palace, while a bit further east in Havel is the Grunewald, a massive forest tract and quite a few rivers and lakes. The great news about Berlin is the amount of green space, with dozens of parks and gardens within the city limits, with famous areas like Botanischer Garten (over 22,000 plants), Wuhlheide Park (forest, amusement park, miniature replica of Berlin and Brandenburg) and Treptower Park (great for walking along and boating in the Spree River) rounding out a long list of fine choices.
Just beyond the city are some great day trip options. Just west is Teufelsberg, a man-made mountain known for its Cold War history. Today it sports great views of the city and a graffitied surveillance post that poses as an intriguing photo opportunity. Southwest of the city is the Spreewald, a vast connection of intertwining canals that paint a quaint picture of a time past. Exploring this area via its waterways is a paramount experience. One of the best ways to explore the state of Brandenburg, which encircles Berlin, is the extensive 66 Lakes Trail, which clocks in at about 400 km (249 miles) long. Starting and ending in the UNESCO-certified city of Potsdam, the trek encompasses the aforementioned lakes and landscapes that vary from forest to plain to rural townships. Finally, the lengthy biosphere reserve that surrounds the Elbe River, which is best explored in the Dessau-Wörlitz Garden Realm of the state of Saxony-Anholt, provides a beautiful selection of parks, gardens, castles, and waterways.
Even further afield, but still within a day trip's distance, is the Baltic Coast. Although not a year round endeavor if you're looking to swim, the area, especially islands like Rügen and Usedom, is a beautiful combination of natural surroundings and tourist amenities. Rügen especially is great for its piers, beaches, and the Jasmund National Park, which includes the picturesque chalk cliffs that look out upon the ocean. The lighthouses and sheer cliffs of Cape Arkona are also quite popular for visitors.
As you can see, there is plenty to do while in Berlin. For more information on specific activities, interact with the embark community or explore our pages further.