(The above image is over Shifu Yan Lei, a 34th generation Shaolin monk who trains outside regularly, much to his benefit.)
Fresh air? Cool breeze? Sunlight? These things have more benefit than being optimal for a fair weathered vacation. Training outside is one of the best ways to detox and revitalize your muscular strength system. The natural world is a gift that we often ignore for the comfort of a home of the convenience of technology. Communication is often limited because of technology; the communication becomes more widespread but progressively less empathetic. In the same vein, our link to all natural things is most definitely interrupted unless we truly experience them for ourselves.
We process a great deal of our information about our environment through our feet. We can detect vibrations through the soles of our feet if something large or potentially dangerous is approaching. We ground ourselves and even get more antioxidants through being in direct contact with nature with our feet.
Shoes and footwear is meant to protect us from many dangers of walking outside, but it also deprives us of the benefits, so training barefoot in nature could give you more health benefits than you might imagine. Research is now pointing to a conclusion that "grounding" yourself (spending time barefoot in direct connection to the earth) will not only help to remove waste products from your body, but also to greatly reduce inflammation.
Doing full, proper breaths outside will do much more for your health than doing the same exercises indoors. Rather than circulating the stagnant air of your coworkers, associates, etc., you will be able to circulate lively, moving air through your system. Your lungs will feel rejuvenated and your body will feel energized as a result. Your endurance will improve, and the fresh air will even help with the development of the muscles in your body!
Feeling the warmth of the sun on your skin can boost your immune system to incredible levels and help you sustain your full health and strength when training outdoors. Vitamin D, one of the best benefits being in the sun will offer you, can boost your energy and immune system. Strength and health cannot be divorced, so training to build one will often develop both.