Even though there's not much online about Jewish personal prayer, far more can be found if the Hebrew word "hitbodedut" is searched instead. The Hebrew meaning is "self seclusion." It doesn't really mean private prayer, but it has come to represent private, personal prayer in one's own language and sincere words.
Some people are intimidated by the use of unfamiliar words, including Hebrew words. So, that's why I say Jewish personal prayer when I describe my experiences with hitbodedut.
Getting out in nature is ideal, but often impossible in our busy lives. Speaking out loud to our Almighty God is what's important, not necessarily where it happens. With one exception...
I know some people may flinch at what I am going to say next, but I know how hard it can be to find a place and a moment to be alone. Unless you are completely desperate, do not choose a bathroom in your home or a restroom in a public place. If you are hiding out for your personal safety, that is a different situation, but if you are merely doing it for your own convenience, just don't do it.
Find a place where you can pray safely and respectfully out loud to God. Wherever you do that, it's hitbodedut, and it's good!