About 30 minutes outside the city is an abandoned spy tower complex called Teufelsberg. Since being decommissioned it has become and artists commune, and is an extremely cool place to explore.

On the far east side of the city, just around the corner from where I work, is Treptower Park. It has many amazing food stands and sits right along the river. It was one of my favorite places to unwind after work, sit, and enjoy the sun. 

Many Berlin U-Bahn stations have very intricate, unique designs. One of my favorite things to do on a lazy afternoon is to take an unfamiliar U-Bahn and see all the amazing architecture and design of the stations.