In a world where cybersecurity is becoming increasingly important and where the lack of workforce is estimated in terms of millions of people, gamification is getting a more and more significant role in leading to excellent results in terms of both training and recruitment. Within cybersecurity gamification, the so-called Capture-The-Flag (CTF) challenges are definitely the corner stones, as proved by the high number of events, competitions, and training courses that rely on them. In these events, the participants are confronted directly with games and riddles related to practical problems of hacking, cyber-attack, and cyber-defense. Although hardware security and hardware-based security already play a key role in the cybersecurity arena, in the worldwide panorama of CTF events hardware-based challenges are unfortunately still very marginal. In the present paper, we focus on hardware-based challenges, providing first a formal definition and then proposing, for the first time, a comprehensive taxonomy. We eventually share experiences gathered in preparing and delivering several hardware-based challenges in significant events and training courses that involved hundreds of attendees.