On June 6th we started a level design contest. July 7th is the deadline and everybody is welcome to submit as many levels as they like via email, webchat or forum. Text and video tutorials are available.
Since releasing the first batch, we received nine levels (one of them in two versions):
LINUX/MAC OS X:
Just copy the path into Explorer's (CTRL + L) or Filer's (CMD + SHIFT + G) location bar to enter that directory.