To hear the hidden song, find and activate the following hidden green rocks. Note: There is no prompt to interact with the rock. The first rock is located in the spawn room at the corner near the Generator Room 3 door. To find the second rock, leave the starting area and go toward Generator Room 2. Follow the route to the workshop through the trenches and locate the sign that points to No Man's Land. Unlock the bunker door, go upstairs, and search under the bunk beds that are against the wall. To find the final rock, open the door to No Man's Land and follow the signs to the Excavation Site. The rock is hidden near some crates that are in a corner of the map to the left of the Excavation Site.
You can kill the giant a number of ways but he can be resistant to some guns. Effective guns include the Acid gat, Death machine, Lsat (with headshots), or a LMG with the Deadshot Daiquiri perk doing headshots. These will usually kill him without wasting too much ammo.
Find the following hidden boxes: the first is located in Freigh's head (the robot over the church), the second is in the staff room under pack a punch (follow the wooden planks), and the final one is in Agartha near the fire staff portal.
For this achievement you must create the turbine, which is composed of the parts in the bus stop at the start (one against the sign in the middle, one beside the bookcase next to the M14, and one on the bench next to the power needed door). Just place the generator at each door of this sort at each stop (bus stop, diner, farm, city, power room). One will not have a part; the other four will. Place the ladder on the back driver-side of the bus, the grill on the front, the emergency ladder on the emergency exit on the inside. If you wait until a zombie destroys the ceiling, you can skip the fourth part. If not, there is a fourth part to attach on the emergency exit.