We had a layover in Germany and stayed in a hotel near the airport. We had been stamped into Germany, Euro zone, European Union and Schengen zone. The European Union and the Schengen zone are not the same, with certain countries participating in each. Then there is the Euro zone, which is the countries that participate in the Euro currency. This would lead to much confusion over the next day and the following week.
The next morning, we mistakenly were stamped out of Germany, Euro Union and Schengen zone after we missed the concept that immigration was only for the gate next to ours.
So, after a delay with our flight, we touched down in Budapest and we essentially were in no-mans land. Because we were flying in from Schengen zone to Schengen zone, we didn't go through immigration to receive another stamp.
Now we were stuck. Not wanting to be considered illegal, we went on a search to find the immigration help desk. In Frankfort's smaller airport, this proved to be an impossible task of being passed along from desk to desk. Finally, the woman at the help desk realized what we were trying to communicate and went in search of an immigration official to check.
My hope was that we could find someone from immigration who would stamp us in to Hungary, showing the same day exit stamp from Germany. Immigration didn't see this as the (logical) solution and instead came back after 20 minutes with our passports to simply tell us to hold on to our entry flight tickets when we get to our next border crossing. Not the answer I was hoping for.
Our next border crossing would come nine days later at the Croatian border via train. Croatia is a part of the European Union but not a part of the Schengen zone (or Euro zone.) We were prepared with our documents, but we'd heard the Hungarian border agents were fairly tough. We had also committed to not bringing up the subject voluntarily, but would provide our documents upon request. It's not that we were scared of truly doing something illegal, it was more the hassle of having to explain to an immigration officer the situation and potentially being asked to leave the train to get through the whole story.
We came into the border town and the train came to a stop to allow Hungarian and Croatian immigration to go through the train.
We held our breath as the man rifled through our passports, knowing our entry and exit stamps were sitting right next to one another.
He lingered on a page. We kept silent.
A swipe of the passport through his handheld and then a loud "CLUNK" of his stamp and we were out of Hungary without a word.
The Croatian immigration agent followed a similar process and we breathed a sigh of relief as we were officially legal again.
The rules are so complicated and each country is responsible for enforcing the laws developed by the treaties and union contracts. It appeared that even local immigration officials can't even keep them all straight.
Our best advice is to be mindful of not overstaying your welcome (90 out of every 180 days in the Schengen zone) and if there is an immigration booth at a gate area, double check you need to be stamped. The rules are just so complicated and while they make sense in the simplest terms, when you are stuck in no-mans land between countries, they become much more difficult to decipher.