1. Five trips to Iraq. More than 15,000 documents. One collapsed “caliphate.”

We published the results of a yearlong investigation, in which Times journalists scoured former offices of the Islamic State that were abandoned by the militants. It shows that ISIS fighters, known for their brutality, were also effective administrators.

We also have a new audio series, “Caliphate,” which followed our reporter Rukmini Callimachi as she covered the Islamic State and the fall of Mosul, Iraq. Listen to a preview here.

The U.S. military, meanwhile, is spending about $1 million on makeshift detention camps for Islamic State prisoners in Syria, broadening its involvement in operations it had sought to avoid.