It is possible for a foreigner to hunt in Poland, according to the Inland Fisheries Act.
- As a citizen of a foreign country you are only obligated to acquire an appropriate permit, which is issued by the owner/leaseholder of the waterbody.
- You can also hunt only during the day, an hour after the sunrise and an hour before the sunset.
- You are not allowed to shoot to both eels and salmonidaes.
- You are allowed to hunt with max 2 prong spear tip with max 3 cm length between the prongs.
- And obviously you have to respect specific protective dimensions.
I think these are the most relevant form the legal obligations. If I overlooked something, somebody please correct me.
As for the suitable places I will not be much of help. I live in a different region, to far from where you plan to stay to have any useful info. Somebody from the Mazowieckie voivodeship would have to assist you in this matter.
I've never hunted in the sea, but considering the amount of videos that I've seen on youtube, it's safe for me to say that it's nothing like spearfishing in lakes. It may be quite a surprise for you If you've never done it, nevertheless I hope you will enjoy it as much as I do