How to find the Training Grounds Key in Phantom Blade Zero

Finding the Phantom Blade Zero Training Grounds Key took me ages, all because I missed a dirt path in the main Mandate camp that leads to the dovecote and, eventually, the boss that holds the key. It's also a very good idea to find it as you won’t be able to finish repairing the Illusory Pipa without it – and you'll miss out on some other rewards too. Anyway, I've explained exactly how you find the Training Grounds Key in Phantom Blade Zero below, so that you can wrap up the Mandate Encampme