One of the places I went was Amsterdam. In Amsterdam they mainly speak Dutch. It was really interesting for me to hear becuase I have Dutch heritage. It is the offical language of all of the Netherlands and Belgium. It sounds very different from Spanish and English because it is a West Germanic language, which means that it is derived from old Frankish dialects, not Latin. However, a couple of Dutch words that are now common in English are coleslaw and cookie.
In Spain and the Netherlands, they use the Euro. In Poland they use the złoty. Their economy is not as stable as those in the Euro Zone so each euro is worth around 4.7 złoty. That conversion doesn't sound too bad, but imagine paying almost 50zł for some chicken nuggets and fries at McDonalds. Also, similar to the USD, there are pictures of important historical figures represented on their notes and coins.
A normal $1 bottle of water would cost around 3,7zł.