Some of the greatest Christian mystics come from this period. One of my favourite books is The Cloud of Unknowing - the author has a spark that you don't seem to get in more modern writers on mysticism. He is as profound as you could wish for, yet he is down to earth, to the point of earthiness, and he has some absolutely hilarious ways of describing the idiosyncrasies of his contemporaries. It's one of the best practical introductions to contemplative prayer that you could wish for, by a very civilised man. I'd love to have met him.