Rostock has an extensive tram network — one of the largest in northern Germany — covering the old town, the main station, the harbour, and the outlying districts. Trams run frequently and are the most practical way to move around the city. The same tickets cover buses, trams, and the S-Bahn to Warnemünde.
The old town itself is compact and best explored on foot. From the Hauptbahnhof to the Marienkirche is about a 15-minute walk. Cycling is feasible — the city is relatively flat — but the old town's pedestrian zones limit where you can ride.
To reach Warnemünde, take the S-Bahn (S1) from the Hauptbahnhof — journey time about 20 minutes.