Lots of people, this is a natural result of continues meditation using visualisation, you see it reliably trained for the most in Remove Viewers (see Lyn Buchannan, Ingo Swann) and the work of Michael Raduga. I think the Monroe Institute courses are also very good. Your main tool is really just practice, lots of daily practice for a years or more, but how long it takes depends on the person.
We put links to Michael Raduga’s free youtube seminar in the Developing Astra senses tutorial collections thread.
These are long but very worth it, as he’s the only person I’ve seen that gets into detailed tips for navigating in the sate and staying in it.