The classic book on working with the energy of the body for spiritual purposes, The Middle Pillar by Israel Regardie, is now more complete, more modern, more usable, and better than ever.
The exercise known as the Middle Pillar was devised by the Hermetic Order of the Golden Dawn. Regardie expanded upon it and made it public over 60 years ago in the first edition of this book. Since that time, the exercise has been altered and adapted for just about any spiritual use you could think of. It is a mainstay of many Western traditions of magic.