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 gaude lines had been built in nowadays western part of Poland. The region, that owns most of these still working is Wielkopolska region. In most cases at least one station of a narrow gauge railway is next to a normal-gauge one, so it;s 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.
Starting from the west :
Gryfice Commuter Line in West Pomerania. Oprates regularly in summer (from gryfice to Rewal, connecting several sea resorts) on the distance of 41 kms.
Smigiel line (Stare Bojanowo - Smigiel - Wielichowo) in Wielkopolska region, phone : +48 65 518 00 10. Regular all-year trains from Stare Bojanowo to Smigiel, additional trains (as well steam trains) od that section and to Wielichowo - on request.
Zaniemysl line (Sroda Wielkopolska - Zaniemysl) in Wielkopolska region. , phone : +48 61 285 82 98. Owned by local authorities, operates on summer Sat and Su from Sroda Wielkopolska (where the trains are coordinated with the ones from Poznań to Zaniemysl. Addidtional trains on request.
Pleszew line in Wielkopolska region. Few daily trains from the centre of Pleszew to nearest normal-gauge line, addidtional trains on request.
Kaliska line (Opatowek - Turek) in Wielkopolska region. Only freight trains are regularly operating, but passenger trains can be launched on request at any time.
Gniezno line (Gniezno-Witkowo) in Wielkopolska region. , phone : +48 61 426 11 30. Trains only on summer Sat and Su, but more can be requsted.
Bialosliwie line in Wielkopolska region. Irregular trains from Bialosliwie (on the normal-gauge line Pila - Bydgoszcz), additional tyrains on request.
Malta children line in Poznań. Regular trains from April to October, in spring and autumn only on Sat and Su, during summer : everyday. Links one of the main public-transport centres in Poznań with the new zoo.
Znin lines (Znin - Wenecja - Biskupin - Gasawa) in Kujawsko-Pomorskie region, , 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 Vth cent BC). Be prepared for kid groups :)
Zulawy Commuter line (Nowy Dwor Gdanski - Sztutowo) in Pomerania