By Frederik Pleitgen, CNN

CNN—Juergen Todenhoefer's journey was a tough one: dangerous, but also eye-opening. The author traveled deep into ISIS territory -- the area they now call their "caliphate" -- visiting Raqqa and Deir Ezzor in Syria, as well as Mosul in Iraq.

 

Mosul, Iraq's second largest city, was taken by ISIS in a Blitzkrieg-like sweep in June.

 

Todenhoefer managed to visit the mosque there where the leader of ISIS, Abu Bakr al-Bagdadi, gave his only public address.

 

And he saw the realities of daily life under ISIS, with all shops having to close for prayers in the middle of the day.

 

"There is an awful sense of normalcy in Mosul," Todenhoefer said in an exclusive interview with CNN.

 

"130,000 Christians have been evicted from the city, the Shia have fled, many people have been murdered and yet the city is functioning and people actually like the stability that the Islamic State has brought them."

 

Nonetheless, he says, there is an air of fear among residents: "Of course many of the them are quite scared, because the punishment for breaking the Islamic State's strict rules is very severe."

 

According to ISIS's leadership, the group's fighters managed to take Mosul with only about 300 men, even though more than 20,000 Iraqi army soldiers were stationed there when the attack was launched.

 

Read More: http://edition.cnn.com/2014/12/22/world/meast/inside-isis-juergen-todenhoefer/index.html