Astral travel is the ability for your spirit to leave your body and travel to other, usually non-physical, plane or dimension. I have only been successful doing this three times in my life and all three were spontaneous.
I have a brother who is able to, at will, travel without being encumbered with his physical body. He is very cautious about the dangers.
Even if you don't believe, you have to find it fascinating. He believes that all past, present and future are now...just in different planes. He describes that the first dimension is the hardest to get through and is filled with murkiness, fog and spirits heavy with emotion. He feels it is very draining and is to be traveled through quickly.
His biggest caution is that time is different on other planes. One direction he can take, and he can experience life on another dimension for weeks and he will have only been gone from his body a few minutes . Another direction and the time there seems minutes and is much longer here....thus the danger of a body left behind to be possibly disturbed by someone or, worse, thought of as dead. He recognizes which way to go now and he does not venture into the time that keeps him away for very long.
He also says that all the fairy tales are true or are vividly imagined and seen on certain planes. There is a real land of fairies and dragons, etc.
There are lands that you don't want to leave and there lies another danger...the longing to stay.
He says all of this is extremely draining on the body, as though you have had a very strenuous workout. Not the way to a good night's rest! However, his wish is to venture into the dimensions and planes of another galaxy or star...since Earth is but one very small spot. Crazy?, perhaps, but he is not limited by beliefs of what lies "out there"....
His frustration is with beliefs that have been installed in him by this world that clip his ability and his wings to do anything imagined.