What did the author find during his travels to the Slovenian Highlands and the Julian Alps as noted in the nonfiction book, Underland?

The Slovenian Highlands and the Julian Alps saw some of the most severe fighting during WWI and WWII. Soldiers tunneled out many of the mountains during the wars and many sinkholes in the region were used for mass murder. As they hike through the beech forests, MacFarlane and his guide Lucian find tons of evidence of the conflicts including swastikas scoured into trees and a poem titled, "Dehumanization," that asks readers to remember the victims of the wars.