I have visited Athens twice so far - in November 2008 and in February 2017. And will gladly return anytime. The city centre is a gigantic historical open-air museum with some monuments dating back more than 2500 years. The food is delicious, people are nice and friendly, the sun is shining most of the time and there is always something new to discover.
A historical city of Acropolis is located in the very heart of Athens at the top of the steep Acropolis hill. This area was reportedly inhabited already in 4000-3000 BC. It's main building - the temple of Parthenon - is visible from almost anywhere in Athens.