By Rick Steves
May, June, September, and October are my favorite months for Berlin — most likely to be not too hot, not too cold. However, these are also the most crowded months; there can be lines at sights and higher prices at hotels.
Summers (July and August) are lively — Berliners love to hang out in parks and along riverbanks, as if enjoying a continuous open-air party. However, the city can get unpleasantly hot and humid. If you wilt in the heat, look for a room with air-conditioning (which can be scarce).
Berlin is a decent winter getaway — its museums are ample and offer an escape from bad weather. However, many of the important historical sights are outdoors. And in general, Berlin is an exuberantly outdoor-oriented city — a scene that wintertime visitors miss out on. Night draws the shades on your sightseeing early, and you'll want to dress warmly, with layers. Expect cold (even freezing lows) and rain (hats, gloves, scarves, umbrellas, and thick-soled shoes are essential).