although data.gov.pl exists, and even presents a valid cert, it has no content. The place with the data is:
https://danepubliczne.gov.pl/en/#
(website is being terribly slow for me right now)
https://www.data.gv.at/ (Austria)
https://data.gov.sg/ (Singapore)
https://www.data.gouv.fr (France)
https://data.gov.be
http://data.gov.ro/
https://www.dati.gov.it/ (note, Italy redirects data. to dati.)
https://data.gov.pl/
https://data.gov.za/ (South Africa's has a cert problem)
https://data.gov.in
https://data.gov.au/
https://datos.gob.mx/