A fire that started Tuesday evening at a vacant Chicago warehouse is now covered in ice after firefighter’s efforts to snuff the blaze.

WGN TV reported the fire was the largest in the city in seven years, at least in terms of response. It took 170 firefighters — one-third the Chicago Fire Department’s firefighters on duty at the time — to put it out. Many were still on the scene in freezing temperatures Wednesday morning.

“I was looking out my window and I noticed the fire, and it was pretty hot, intense,” Bridgeport resident Mike Lopez said to WGN TV. “Then this morning, my son wanted to come and look at it, and it looks like an ice castle.”

Watch WGN TV’s raw footage:

WGN TV reported that the cause of the fire is under investigation.

Here are photos showing both the blaze and the icy morning after: