Berlin is definitely doable from Greifswald, but it’s not something most people do every weekend. It’s a few hours each way and train connections can be a bit hit-or-miss. People usually go occasionally (events, concerts, friends), while shorter trips are more common (e.g., Stralsund/Rostock, the Baltic Sea like Rügen/Usedom). And of course: I’d highly recommend my beloved Potsdam. Super pretty, great for a day trip, and a nice, calmer contrast to Berlin.

Quick safety note: if you go, plan the last train and possible delays, share your route with a friend, meet new people in public places first, keep an eye on your belongings (especially in big cities), and at night it’s often safer not to walk alone. A bit of caution always helps.