Sending out enciphered postcards is great fun. The hackers at Entropia have published a set of cards on their website. Some postcards have already been deciphered, others are still undisclosed.
The Gpn is a yearly scene event in Karlsruhe. Hackers, crackers, geeks, nerds and other technology lovers meet there for three days and share ideas and source code. There's a conference track, nice ambiance and interesting people.
official wiki
