So let's move on to natural environment, because you seem to think it's a difference between "outdoors" and "indoors".
All organisms are designed to live in a certain type of environment. Fish, for example, are designed to live underwater, and will die if you remove them from it. Likewise for marine mammals. Furthermore, those animals designed by nature to live in water can only do so in certain types: some can only live in freshwater, some only in salt. Some can only live in water at lighter pressures (near the surface, in other words), some are designed to live with greater pressure. If you remove any of them from the environment they're designed for, they will die.
Human beings are land animals, designed to live surrounded by air and subject to normal land gravity. If you remove a human from an environment surrounded by air, he will die. Likewise, if you remove humans from normal land gravity for any great length of time without compensating technology, it is also detrimental to their health and potentially life-threatening.
Also, land animals are designed for different types of environment on land. While penguins, for example, can survive quite happily in Antarctic conditions, very few other animals can without technological compensations. Meanwhile, penguins cannot live outside of that environment without human intervention.
Meanwhile, some animals are designed to live in one type of environment at one stage of their life cycle, and another at a different stage. Most tadpoles, for example, are aquatic. During that stage of their lives, they cannot live outside of water. When they leave that life stage and metamorphose into frogs or toads, their natural environment changes.
There are many species of organism for whom their natural environment is the body of another organism. If you remove them from that environment, they will die.