A hidden gem in this instance could be anything that is an "unknown unknown" where most people not only don't know the specific thing itself, but the whole type of thing. So a "known unknown" would be a shirt because we know about shirts, but we may not know about the specific shirt that is so valuable to you. So don't include anything like that. Try to write about something whose whole purpose is unknown to many people. For me, a hidden gem would be "super sour morning shots" where you drink a small shot of something so intense it wakes you up really well and it can be really healthy. I drink lemon juice with ginger and it works great. Feel free to make multiple entries if there's more than one that you can think of. Winner is determined my likes so make sure to look around and find the hidden gems that you like the most.