There are plenty of fascinating places to visit in Europe. London is really popular, but a lot of Polish inhabitants never been there - when you don't also, you should change it. On the other hand we have Serbia, beautiful country with sad history, for sure worth to be explored.
Since past decade Polish citizens had a chance to tour whole around the old continent without spending too much money on this trip. Nothing surprising in that, cause since then prices of airline tickets are in very attractive price.
Although there are plenty of amazing places in the world, which you should see, there are two which are particularly interesting. Maybe it would be a good idea to visit them during the upcoming holidays?