Poland, which is the only member of the 25-country "Schengen area" not able to travel to the United States without obtaining a visa in advance. This process is long and costs Poles a lot of money for just a slight chance at hopefully obtaining a visa.
As a member of the Schengen area, and a strong Ally to the US this is a ridiculous that Poles need to go through this entire process for only a slight chance of being allowed to visit.
Obama has promised Poland that during his Presidency.