The apartment destined for the purpose was spacious and lighted by a number of windows, over each of which was written in golden letters for some inexplicable reason the name of one of the principal cities of France; beneath these windows a wooden balcony extended the entire length of the house.
There are no more uses of "inexplicable" in the book.
Show samples from other sources
With that he turned away and once again started inexplicably walking toward the wall.
James Dashner -- The Scorch Trials
For some inexplicable reason, those words popped into Thomas’s mind.