This German-based bus company is the largest in Europe, and arguably the best bus service in Poland. With over 2000 destinations in Europe, FlixBus can get you to practically anywhere in PL, plus other popular nearby destinations like Vienna, Prague and Berlin. All buses include free wi-fi, toilets, and seatbelts, and leave from the main bus station. Schedules change too often to list here, but visit their easy to use English website for booking and full details.
