Entry and stay
German require only a passport or by entering the country by airplane only an identity card. A visa is not required. The citizens of some countries require for Turkey a visa that is given however problem-free by entry.
Basically you may stay as a tourist without special permission up to 90 days after your entry in Turkey. This permission can be extended to your proposition there by the responsible Turkish authority for further three months. To extend your stay, please contact the responsible authority there in time, before the 90 day deadline has passed.