I may be caricaturing myself by recommending a summer book that is a) hard to find, and b) obscure in subject matter.  Nevertheless: I recommend a search for a book called The Zohar in Muslim and Christian Spain, by Ariel Bension.   It can be encountered in the odd Judaica store or online at www.abebooks.com.  

This volume is unique: the only extended commentary by a 20th century Kabbalist on the relationship between Kabbalah and Sufism, i.e. Islamic spirituality, with especially interesting remarks on the greatest of all the Sufis, Muhyid’din Ibn ul-Arabi.   R. Bension goes further than either Gershom Scholem (who cited him), Moshe Idel, or any other modern Jewish scholar in this direction.   His book also illuminates the links between both Kabbalah and Sufism and Spanish Catholic mysticism.  The author was a Sephardi born in Jerusalem, and the first Sephardi from the Holy Land to study in modern European universities.  He was a rabbi in Manastir, one of the Sephardic and Sufi centers in the Balkans, where Jews frequented the Sufi assemblies of their Albanian and Turkish Muslim neighbors.  The book is extremely readable, and a good introduction to the Zohar.