The vast majority of visitors in Greece in 2007 came from the European continent, numbering 12.7 million, while the most visitors from a single nationality were those from the United Kingdom, (2.6 million), followed closely by those from Germany (2.3 million). In 2010, the most visited region of Greece was that of Central Macedonia, with 18% of the country's total tourist flow (amounting to 3.6 million tourists), followed by Attica with 2.6 million and the Peloponnese with 1.8 million. Northern Greece is the country's most-visited geographical region, with 6.5 million tourists, while Central Greece is second with 6.3 million. I want to ask Which part of Greece is the most visited? If you can't find the answer, please respond "unanswerable".
Central Macedonia
The context describes the number of visitors to Greece by both region and nationality. It mentions that Central Macedonia contains 3.6 million tourists, which is 18% of total tourist flow in all parts of Greece, making it clearly the most visited region within Greece as a whole.