If this type stuff interests any of you but is too hard, give mine a try ( 0x0539.net ). It is not intended to be a significant challenge, instead all the stages focus on introducing some basic concept related to offensive security. Its mostly aimed at some young teens that have expressed an interest in learning that stuff rather so the target is very introductory.
I update the site every so often with new sets of challenges and rotate through former sets if someone requests it. The current one I ran for a bit in 2013 and then brought it back earlier this year and plan to cycle in a new binary exploitation focused one in December.