Hardware capture the flag puzzles, artistic PCBs and #badgelife with Uri Shaked from Wokwi and Helen Leigh from Crowd Supply. Uri Is the creator of The Skull, a Capture the Flag (CTF) riddle that invites you to explore the internals of the AVR architecture.
The Skull has multiple stages and will likely keep you busy for days, or even weeks, as you exercise the muscles in your brain and apply them to the riddle in hers. Unless of course your mind slips its grasp on reality and you tumble, unmoored, into the swirling, lunatic void. In which case you might be at it a while longer. In order to keep your sanity intact, you will need three things: the ability to read and understand Arduino code, a willingness to spend some quality time with the ATtiny45 datasheet, and basic programming skills.