Northern Germany is warm in summer and cold in winter, although cities such as Berlin are popular no matter when you visit, unaffected by the climate.
The centre of the country is wine making land, and basks in lovely hot weather throughout the summer, while the south is popular with skiers and mountaineers in weinter and summer respectively.
Many of the cities in germany, most notably Munich have large beer festivals such as the famous Oktoberfest, which take place in September every year, and are a good time to visit the country for a heavy session on ice cold strong lager while listening to Oompah music. The experience is usually quite in tents!