Dyatlov Pass for me too. Ive yet to see a explanation that fully encompasses every aspect of that event.
...and dont direct me to the Cracked article. You do know its a humour website right? Its not an actual reference. Also, The Bloop
Also The Tamud Shaw Case/Somerton Beach Mystery. Full of WTF. And the Beaumonts. A hundred suspects, not one actual answer.
And lastly a more obscure one from Australia...Nancy Insitori. Murdered in NSW in the 30's, the then insular and closed off nature of Italian migrants heading off investigation. Possibly related to early Nrdrangheta/Calabrian mafia cells, but who knows?