I'd be careful with a lot of these blanket statements in this thread. Don't know about polish law, but in this western european country any airfield outside it's operating hours - be it controlled or uncontrolled - has same legal status as a barley field or the Autobahn with respect to airlaw. Departing or landing is not a misdemeanor but a criminal offence although the facilities may be perfectly suitable to do so.
GA wise many pilots especially from the island don't know and are so courteous to drop a fiver and slip with their registration and landing/departure time in the letter box. Very bad idea. At least don't get caught.