Built as a green space for locals, Treptower Park came into its own during the city’s division, when it became one of East Berlin's most popular outdoor spots thanks to its riverside location and a nearby (now abandoned) theme park. Today the centerpiece is the gigantic memorial that commemorates the 300,000 casualties suffered by the Soviet Union during the Battle of Berlin in 1945. Some 5,000 bodies are buried beneath the memorial, and part of the main statue repurposes marble from Hitler’s Chancellery. The harbor area makes for pleasant ambling and leads to the charming Insel der Jugend (Island of Youth) and the forested Spreewald farther along the Spree. You can also explore the Haus Zenner restaurant and beer garden for refreshment, or visit the Archenhold Sternwarte, an observatory with the world's longest refracting telescope.