Negative PCR tests needed
For instance, in most countries (For example, Greece, Bulgaria, Estonia, etc.), you need to show negative PCR tests. Those tests have to be up-to-date. Greece is asking for the PCR test result of the maximum 72 hours. It means that you can take a PCR test maximum of 3 days before the entry. Follow the specific rules of each country because they may ask for PCR tests and vaccination too.