Almost every café in Berlin that has wifi: Ask for the wiki password at the bar, or find it next to the menu card, or at some wall.

The only problem is that many cafés / bars don't provide wifi, because they are afraid of providing wifi at all due to the "Störerhaftung" (a legal issue that exists almost nowhere except in Germany). Luckily, there's Freifunk and VPNs to the rescue.