Hidden bonuses: 3
Level walkthrough: Head forward and keep moving towards a large building located in front of the entrance. Make a jump towards the scaffolding and head upwards. Make sure not to lose balance and fall, because ending up in the water could result in the main character dying. Approach the entrance to the building.
As you've probably noticed by now, the first bonus item is floating above your character. Stand under the object and reel yourself in to collect it. Head on to the next section and take a moment to watch a tutorial movie. Once it's over approach a fork-lift truck. Lift the machine in the air (Y), jump (A) and punch it (B).
If you've done everything according to the plan you'll see that a large hole has appeared in one of the nearby walls. Obviously you'll be allowed to jump through the hole to get to the next section of the map. If you've missed, perform the exact same actions with one of other blinking objects. Make sure to choose grenades from your inventory before moving on.
A large group of enemy soldiers is stationed just around the corner and I would recommend using grenades to get rid of them. Ignore a new bonus object seen along the way, because you'll return to it later on during the game. Keep heading forward and eliminate single enemy units as you go. Retreat behind the corner when you encounter a larger group.
Make sure to eliminate all enemy troops before moving on, because a Biomech is waiting for you in the next corridor and you'll want to focus your attacks on the metal beast. Thankfully winning shouldn't be a problem. Once the mech has been eliminated inspect the area in front of you and gain access to the upper balconies.
Locate a passageway next to large pillars and eventually you'll find the second bonus item. Once this object is in your possession return to the main corridor. Head down and begin moving forward until you reach a new warehouse. You'll now have to throw a fork-lift truck at the wall, so you'll unlock the exit.
Make sure to use your bionic arm to attach yourself to metal bars along the way. Eventually you should be able to get to the crane and from there you'll be allowed to jump to the third bonus item. You must release the hook at the very last second and you also have to prevent the main character from drowning. Once you've taken the item proceed towards a nearby tunnel.