Destroy turrets in sewers was a mission in Jak II. Krew had some other job for Jak this time and promised him a weapon upgrade in return. Jak had to go into the Haven sewers and destroy the sentry guns Baron Praxis had installed as security devices, so Krew could continue his 'smuggling'.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Turrets Syndrome", completing this mission will reward you with a bronze trophy.
The Sewers are filled with glubs, znorkle tooths and a number of grunts; new Metal Heads similar to the manic head only a bit faster and stronger. For starters move ahead and activate the button here to turn on some lights, right around the corner is your first sentry gun (identifiable by the sound it makes when it turns and fires). Zig-zag and jump towards it until you're close enough to hit it with the Scatter Gun.
Move on through the Sewers until you reach another sentry gun (past the first three grunts), take this one down as well and then go back and head left onto the metal walkway. As soon as you make a few steps however, it will break down and collapse forcing you to the enter the following room from the ground. Turn the corner and you'll see a large number of skull gems and eyes glowing in the dark with a button nearby which you should press for some light.
For this fight you can either rely on the width of the Scatter Gun to knockback (and keep knocked back) the grunts that will come at you or use Dark Jak (and if possible; Dark Bomb). Shortly after this there'll be another sentry gun for you to destroy. Next is a corridor in which the light stops working, forcing you to fight three more grunts in the darkness (though you can push them out of the corridor with the Scatter Gun and let the sentry gun kill them for you).
The path is now open to the last sentry gun, so go on and destroy it. The path afterwards leads back to the elevator at the entrance though you'll be ambushed by two more grunts before you can leave.