There is an airport in every large Polish city. There are more international connections (especially low-cost airlines) rather than national carriers, but this has been changing recently. For example, you can get from Krakow to Gdansk in 1 hour (for about €25).
In Krakow, in order to get from the airport at Balice (officially known as the Pope John Paul II International Airport) to the city center you have a choice of routes:
By train – about 20 minutes from the main railway station in Krakow, which is a 10-minute walk from the Main Market Square; the price of the ticket is about 10zł; tickets can be purchased on the train from the conductor.
By bus – about 40 minutes to the Central Station, the price of the ticket is about 4zł; tickets can be purchased on the bus from the driver, at a vending machine, or at any ‘kiosk’ in advance.
By private bus or taxi (the most expensive option)