That some skills cannot be learned on the mats is an uncomfortable truth within many martial arts. If your martial art is to be used outside the confines of the dojo, then it should be trained outside the dojo.
The simplest footwork can be undone by an unpredictable surface, with obstacles and fluids conspiring to break your form. So we need to go outside, train in the woods, on concrete, in gardens - and not just in the summer! There's an interesting section in 'History and Tradition' about training on ice to develop good balance, ukemi and structure. While the photo in the book could be better it gives a sense of what is meant.
Training in the cold and the wet, doesn't sound like fun, but it will pay off dividends. The unpredictable nature of the surfaces will illustrate why you need to have a lower centre of gravity, to bend your knees and be aware of your feet. Far better than practice solely in a well lit dojo.
A small example can be seen in ukemi (rolling) that is used in ninjutsu as a means of escape, a means of absorbing blows and falls, and as a way to improve your overall taijutsu (body dynamics and movement). You need to be able to do that on any surface - not just a padded mat. Its interesting to realise that rolling on concrete is actually better than rolling on lino surfaces. It seems that the more shiny or glossy the hard surface is the more it challenges your ukemi. The softer the surface the more it absorbs the momentum of a roll, it makes it more challenging to complete the motion into a useful kamae or posture to react from.
As you train you find some interesting insights about how some of the tools and clothing in traditional ninjutsu work better in the wet. When you get brand new tabi (the Japanese ones) the cotton soles are slippery on mats - but if you get them damp they suddenly have grip. The rope of the kyoketsu shoge (hook knife with a rope and metal ring) works better to entangle and snare an opponent when its wet. The iconic 'ninja' mask will filter smoke better when its wet. This art, it seems, works better in bad weather.
And not only cold and wet, but in low light as well. If we are to get a useable skill for this art the ability to apply techniques by feel and in the dark is essential.
So get outside and try simple ukemi, in the wet, in the cold and dark. See what changes when you train on a slope or in a wooded area. This will all point out, without any filters, where you need to improve. You will see how these conditions affect your movements, how the cold can cause a reduction in the movements and dynamics of the techniques. It will show you how some of these techniques work, when they seem impractical in a well lit dojo environment.
Become comfortable in being uncomfortable...