Santa Teresa de Jesús, a Spanish mystic in the late middle ages, authored two books that guide how to enter the deepest mediation for approaching and being literally united with Christ. Those books are "Camino de Perfección" and "Castillo Interior o Las Moradas". I pretty much feel easier to read the former one rather than works by St. Juan de la Cruz, who is another mystic at her contemporary and worked very closely with her for reformation of the Carmelite community. The way of her description is more straight than his and very narrative to have you see what is going on in her mind.
A good news of her works is that even scientists get better off with her instructions on the way of living. Especially, your surroundings or even strangers against your ideas about new topics may often annoy you with their critics. In that case, you would find a good way to endure them in her following passage: It is trial that should be always accompanied with any creature on the earth (Castillo Interior VI-1-3). It's true. This is a good book to read for true researchers who would like to find gloria outside themselves.