Polish narrow gauge railways are mostly short sections of old sand-, beetroot-, mine- or simply commuter railways constructed mostly at the turn of XIX and XXth centuries.
Due to economical changes in 1990s, many of the lines have been closed or even dismantled, however some of then are still operating. As - generally speaking - Germans used to be more fond of railways (while Russians and Austrians less) most of the narrow gauge lines had been built in what is nowadays the western part of Poland. The region that owns most of the still working lines is Wielkopolska. In most cases at least one station of a narrow gauge railway is next to a normal-gauge one, so it is easy to start a narrow-gauge adventure getting there by regular train.
Be prepared, that in many cases local narrow-gauge lines operate only in summer (May-September or even the end of June till the end of August) and during some weekends, so they aren't used for regular passenger traffic any more. But there are still some operating daily, or at least on schooldays.
- Upper Silesia line (Bytom - Miasteczko Śląskie) in Upper Silesia region 
- Gryfice Commuter Line in West Pomerania . Operates regularly in summer (from Gryfice to Rewal, connecting several sea resorts) on the distance of 41 km.
- Gniezno line (Gniezno-Witkowo) in Wielkopolska region. , phone : +48 61 426 11 30. Trains only on summer Sat and Su, but more can be requested.
- Kalisz line (Opatówek - Turek) in Wielkopolska region. Only freight trains are regularly operating, but passenger trains can be launched on request at any time.
- Śmigiel line (Stare Bojanowo - Śmigiel - Wielichowo) in Wielkopolska region , phone : +48 65 518 00 10. Regular all-year trains from Stare Bojanowo to Śmigiel, additional trains (as well steam trains) od that section and to Wielichowo - on request.
- Środa line (Środa Wielkopolska - Zaniemyśl) in Wielkopolska region.  [dead link], phone : +48 61 285 82 98. Owned by local authorities, operates on summer Sat and Su from Środa Wielkopolska (where the trains are coordinated with the ones from Poznań to Zaniemyśl. Additional trains on request.
- Pleszew line in Wielkopolska region. Few daily trains from the centre of Pleszew to nearest normal-gauge line, additional trains on request.
- Białośliwie line in Wielkopolska region . Irregular trains from Bialosliwie (on the normal-gauge line Piła - Bydgoszcz), additional trains on request.
- Żnin lines (Żnin - Wenecja - Biskupin - Gasawa) in Kujawsko-Pomorskie region,  [dead link], phone : +48 52 30 20 492. Regular courses several times a day from Znin to Gasawa, calling at Wenecja (a narrow-gauge open-air museum) and Biskupin (the excavations of an old settlement from 5th cent BC). Be prepared for kid groups :)
- Żuławy Commuter line (Nowy Dwór Gdański - Sztutowo) in Pomerania 
- Rogów commuter line (Rogów - Rawa Mazowiecka) in Łódzkie region 
- Piaseczno narrow-gauge line in Mazowieckie region 
- Sochaczew museum line (in the narrow-gauge open-air museum) in Mazowieckie region 
- Mława line in Mazowieckie region
- Starachowice - Iłża line in southern parts of Mazowieckie region 
- Ełk Narrow-Gauge line in Warmian-Masurian Voivodship  [dead link]
- Nałęczów - Opole Lubelskie line in Lubelskie region , 50 km
- Jedrzejów - Pińczów Commuter Line in Świętokrzyskie region 
- Przeworsk Commuter line (Przeworsk - Dynów) in Podkarpackie 
- Bieszczady forest line in Podkarpackie, 33 km 
- Białowieża forest line in Podlaskie region, 17 km
- Kozienice forest line in Mazowieckie region
- Wigry forest line in Podlaskie, 10 km  [dead link]