It's the Polish national domain.
Example: Copernicus

UPDATE:
Polish Domain Search is the place to start
I checked for perlmonks.pl there and it's definitly available. Looks to me that there are 23 polish domains so far. This may mean that there is a restriction on who can own the domain. I know in Italy you have to be a citizen or a firm based there.
I looked at the fee page and if anybody could tell me how much 800 PLN is? I assume the 22% VAT is Value added tax.