I've previously expressed regret that I hadn't read some of these books before one of the initiations, and Geshe Sopa's The Wheel of Time: The Kalachakra in Context is certainly like that ... I would have definitely gotten a lot more out of these experiences had I had the "framing" of some of these books ... unfortunately, the timing just wasn't there for me! This book is credited to Geshe Lhundub Sopa, who is the director of Deer Park up in Madison, but it is actually a collection of several essays by him and a couple of western students (with a foreword by the Dalai Lama) on various aspects of the Kalachakra.
Now, if you've not encountered Vajrayana Buddhism (which would be most people), it's very much based on visualizations (as I've often joked, most Tibetan Buddhism comes from guys who spent years in tiny cells on mountainsides staring at a blank wall), and to fully "get" the Kalachakra Initiation ...
"One is said to have accomplished the generation stage of the Kalachakra when one can visualize the entire mandala in a drop the size of a mustard seed at the tip of one's nose, with such clarity that one can see the whites of the eyes of all 722 deities - and can maintain this visualization with uninterrupted one-pointed concentration for four hours."... needless to say, few (of the thousands who attend these events) come even close to having that level of practice! However, the Dalai Lama has said that one of the reasons for doing such large ceremonies (the ones I attended had about 3,000 but some of the Indian ones have had over 200,000 there!) is to provide the necessary karmic connections to students who in a previous existence had done the work but had not been able to attend an initiation to get the "permissions" (on a mystical level) to unlock the practice.
One thing that I had not "gotten" from attending these was the "prophetic" nature of parts of the Kalachakra tradition. Now, "kalachaka" translates to "wheel of time", so this is not a big surprise, but I found it fascinating to see some of the specifics. One of the prophesies involves the near-destruction of the Dharma by "the barbarians", a group that closely parallels the Muslims, with the "mantra of the barbarian deity" being bi si mi lla, remarkably close to the Arabic bismillah, "in the name of Allah", and the "name of the barbarian deity" being rahma na, similar to al-Rahman, "the Merciful", an Islamic name for God ... thankfully the prophesies end up well, with armies from Shambhala crushing the barbarians and establishing a new golden age.
I've always recommended the Vajrayana visualization practices as a very useful tool in any mystical tradition (I've found the techniques especially useful in Shamanic work), so this is a book that might give you some ideas, even if you're not particularly interested in the esoterica of Tibetan Buddhism! The Wheel of Time is still in print, so you should be able to get it from your local bookstore, although "new" copies are available via the Amazon new/used vendors for somewhat over half of current cover price.