Poland's economy is booming, but the Polish stock market is not. I mean, it peaked in 2007/2008, and hasn't been able to beat that All Time High since.
One of the problems is that for smaller economies (including Nigeria, below), investing requires local knowledge. A US index fund will roughly track the US economy. The 20 largest local companies in Poland? Not so much.
In other words, it's a place for active trading. Investing in the former Soviet companies at the time of the collapse of communism would have been a bad bet (but reflected in the WIG20). Investing in the startups displacing them? Great bet.
Real estate too. Having Polish land valued at a tiny fraction of German land in 1990 was clearly not long-term sustainable.
My expectation is that the Polish per-capita GDP will reach that of Western powers in at most a decade or two, which gives a natural 4x return over baseline. It's not the astronomical return of post-Soviet era, but it's still large.
In other words, smaller economies are a good place for active trading. I don't do it since if I did without local knowledge, my returns would be similar to the 1x of the WIG20, rather than the 10x of active traders in Poland.
https://stooq.com/q/?s=wig20&c=20y&t=l&a=lg&b=0