Have you ever tried inverted corridors? I find them great way to create sections with uncertainty, to get used to ignore something, to force you to use compass and also to get used to run by features instead of running dead on or over them (something you often need to do in races to avoid unnecessary climb or with features that slow you down).
I personally find inverted ones more interesting / challenging / meaningful than these regular old school corridors. At last for a change.
I have never tried it yet, and it seems hard to give an opinion then. For sure, it looks challenging.
it is important to get the challenge / difficulty level about right. In practice designer has to think how navigation is supposed to be done and which features used. Drawing the empty corridor the way those features can be seen both on map an in forest. Sometimes you draw the corridor by or around those features, sometimes straight to them and make turn just if front of them (so runners can look straight ahead and aim dead on them with compass and just make turn when they see it).
It is easy to design bad ones. It should not be white paper bearing exercise.
I loved your explanation of why corridor training is useful! You pretty much summed up all of my weaknesses in that, so I'll definitely have to organize some for this spring! Thanks!