Hi Daniel,
I am an american living in Prague and had been working in commercial real estate for about 8 years before moving into another area. What kind or rentals are you looking for? Residential? Commercial (Office, Retail, Industrial, Hotels, other)?
When I first arrived the residential rental market was booming and it was still possible to earn decent rental returns as properties were much cheaper. Fast forward 13 years and residential properties have appreciated tremendously. Rent have also increased, but not as fast. Interest rates have been low and demand has outstripped supply now for a while. As for commercial real estate, it has matured and become a much safer investment than when I first arrived. There has been a lot investment transactions over the past 2-3 years, but the market seems to be cooling a little. While I cannot comment on Poland as much, they have experienced similar growth as in Czech Republic. Also, like Prague, Krakow is a beautiful city that receive a lot of tourist traffic. I hope this helps.