I happened to be in Wroclaw on the day of the Polish flag. The flag like it is today existes since 1919, shortly after the Second Polish Republic was founded. Since 2004, the Day of the Polish Flag is celebrated.
Comments and suggestions are much appreciated!
Here are my get pushed-challenges
Update 05/2019: Year 3 begins! I'm living in Bremerhaven near the North Sea since October...