Dying Light

Quarantine Zones are little areas that are cut off from the open world of Dying Light. These places are generally signified by caution tape, lots of ambulances, or in the case of some of the Old Town locations, the entire building is in a big yellow tent. Inside these areas you will find various trials, consisting of either killing all of the zombies, or collecting all of the air drops, and usually tackle one or two other obstacles at the same time (such as choking smoke, noxious gas, or Volatiles). There are a total of 8 of these zones in the game: 5 in the Slums and 3 in Old Town. The Quarantine Zones won’t actually appear on your radar or map until you are very close to them, making them somewhat difficult to find without a guide.

NOTE: Keep an eye on your achievement tracker before and after you first enter a Quarantine Zone, as you may find yourself getting credit by just entering the area, allowing you to just turn around and leave without actually clearing the zone. Thanks to mnwlkr for pointing this out. Full credit to PowerPyx for the video below, which shows the location of all Quarantine Zones.

Below is a text description of each zone's location, for those that prefer text. Keep in mind that describing some of the locations in words can be difficult, but if you get to the general area you should be able to see the quarantine zone pretty clearly.

Slums
Bright Mountain Tunnel
Location: Located through a doorway in a train tunnel at the South side of the slums, near the middle of the map.
Notes: You will need to find 5 air drop packages in a long train tunnel. Considering how long it takes to open the train cars and search, I recommend having the survival skill that allows you to use zombie nastiness to camouflage yourself, allowing you to frolic through the tunnel unmolested.

Chemical Storage
Location: South Westernmost part of the map in one of the warehouse buildings. The biohazard icon will appear just above the Bolter icon.
Notes: The second room is full of noxious gas, so you basically need to play the floor is lava and stay off the ground. This is made a bit more difficult by the many Spitters in this room.

Stuffed Turtle
Location: On the North side of the shopping center that is just North of the highway that cuts across the middle of the map.
Notes: The floor in the first room is electrified, so you probably want to shut off the electricity, then let all of the zombies in. Be wary of the Bomber behind the swarm of zombies, so clear the group from outside the room they are in.

Underground Parking
Location: Immediately NW of the Stuffed Turtle, on the back side of an apartment building is a staircase into the basement parking
Notes: If you can’t handle a single Volatile DO NOT enter here. While all of the Quarantine zones are labeled as Hard, this one can actually be Hard, with around a half dozen Volatiles inside.

Sunny Apartments
Location: Roughly straight West (a tad SW), on the East side of a building going parallel with the N/S road. Note the police van in front of the building.
Notes: Be aware that as you choke on the smoke, you will occasionally lose large chunks of health.

Old Town
New Antalya Apartments
Location: Along the Southernmost wall of the town. It’s in a huge yellow quarantine tent.
Notes: Nothing overly special here, just a bit trickier to navigate the narrow hallways.

Parking Lot
Location: West end of the Southern part (below the river) of Old Town. This is near Dr. Camden’s lab, and NW of where you exit the sewers from the Slums.
Notes: Watch for Bombers and accidentally blowing yourself up on one of the many barrels and propane tanks.

Striped Dragon Hotel
Location: On the same block as the crazy prophecy guy on the North side of the river, the entrance is also facing the river.
Notes: Yet another apartment. I think there may be a Screamer in here as well.