The Acropolis - Cut Short Challenge

The second market stall on the west side of the bazaar contains a small, hard-to-spot walkie talkie (1/6) hanging by a cord. Use Survival Instinct if you're having trouble finding it. As long as you've unlocked the Eye for Detail skill, it will glow.

Shoot this radio.

Destroying it initiates the Cut Short Challenge, for which you must find and destroy 6 of these devices.

There are 3 walkie talkies in the MARKET SQUARE WITH THE WELL, where you fight the first group of trinity soldiers. The first walkie talkie (2/6) is hanging beneath the yellow-and-white awning on the east side of the square.

There's another walkie talkie (3/6) in the stall with the baskets of fruits and vegetables on the west side.

The next walkie talkie (4/6) is in the stall in the southwest corner, on the left just before you exit the MARKET SQUARE.

Later, during the section where you fight your way through the streets to reach the tower, you'll find the next walkie talkie (5/6) in the area beyond the metal barrier you have to blow up with a grenade. It's hanging beneath the canopy on the left. (It is also shown in the screenshots for that section.)

The last walkie talkie (6/6) is hanging in the market stall near the Tower Courtyard Base Camp, along with a document and some gold coins. (It is also shown in the screenshots for that section.)