This is a page that has some cool free christian books that you can read/download.
The first few books are about visits to heaven, heavenly visitations, and different testimonies from heaven given by people who went there.
The book “40 Days in Heaven” is an awesome book about Seneca Sodi’s 40 days in heaven and what he experienced. The book is pretty wild in some of it’s content, but I thought it was very edifying and has some really great revelations in there. Seneca got to talk with many of the saints from the Bible like– David, Abraham, Paul, and more. It was very interesting to be able to hear the responses they gave to some of the questions he asked them. As well as the different realms of heaven, and the way things function up there. Pretty awesome stuff! You can read it online here: http://40daysinheaven.com/
Here is another one you can read online that is pretty short, it’s only about 60 pages. Oden Hettrick go to visit heaven many times (he stopped counting after about 80). He recorded just a small bit of some of his experiences and knowledge from all the many times he got to visit heaven. This is the record of those revelations that he passed on to his family: http://www.odenhetrick.com/read.html
Peter Tan got to visit heaven a number of times during a brief period of his life, and God showed him some really incredible things. During his visitations of heaven, he was shown many powerful revelations of Jesus, the throne, and how heaven operates. You can download the pdf for this book here: http://petertan.net/newsite/books-spiritualworld.html
Some non-free books about testimonies from heaven that I recommend are: Heaven Awaits the Bride by Ann Rountree
Revealing Heaven by Kat Kerr