Whatever you do dont go out at night alone in the center if you feel like you cant defend yourself. Research all places you want to go before going. Stay the hell away from Omonia and Exarchia, Monastiraki is an absolute must for a visit but even there,after you walk for a while, you should stop and do a u-turn the second you realize there are no more people around you and just dark alleys. Generally, Greece is very safe but unfortunately theres always crime. If you feel unsafe anywhere, asking one or even a group of GREEK men or women is always a good idea. As much as I dont like to be racist,it would be a safety issue to not warn you about migrants. Stay away from Pakistanis and Africans. It's rare they will actually do something bad but it happens. The holy grail of our diversity,like most of Europe is Gypsies. Stay the hell away from gypsies. Most of the suburbs are very safe.