The new Season 2 brings with it some changes to the Warzone map, including a new POI called 'Shipwreck.' This shipwreck is located at the shores of Verdansk just south of the Prison. This ship holds "dark secrets," one of which includes Zombies.
You can complete a certain side-mission to earn some great rewards that can shift the balance of the game in your favor at the ship. To get to the rewards, you need a Yellow Access Card that will open a yellow crate located inside the ship.
To get the Yellow Access Card, you complete the side-mission. To start the side-mission, make your way to the shipwreck and enter the ship from the ship's western end, where it has been separated due to the wreck. There will be a huge opening to enter the ship.
Once inside, you will find a set of stairs to your right leading up to a platform.
Go up, and you will find a machine that resembles the trial computer from the Black Ops Cold War zombies.
You can activate this machine that will cause hordes of zombies to attack you.
You must kill 40 zombies in total. A red skull icon will appear next to your mini-map, indicating how many zombies you have killed.
Kill all the zombies, and the 40th zombie that you kill will drop the Yellow Access Card.
Pick up the access card, and a yellow icon with a skull will appear on your screen and mini-map, which is the yellow crate's location with legendary loot inside it.
The chest is always in the same place, just past the machine in a room with many barrels containing Nova 6 gas.
There will be a locked door leading into the room with the crate. The door only opens up once you have acquired the Yellow Access Card It won't be hard to locate as it will be shown on your screen.
Use the Yellow Access Card to open the crate, and you will get legendary loot, including a guaranteed armor satchel and durable gas mask drop. If you're playing plunder, then you won't get the durable gas mask, but instead lots of cash and scorestreaks.
You can repeat this as many times as you like, but it is not as simple as it seems as other players also try to complete this "trial" to get a chance at that yellow crate. Once you activate the machine and the zombies start spawning, the number of zombies is counted even if other players kill them.
Be very careful when killing the zombies. You must be the one to kill the last zombie, as it is always the last zombie who drops the Yellow Access Card. A quick tip is to wait until the kill count has reached 38-39, then kill one or two zombies to get the access card. The shipwreck is a hot zone and the majority of the players are drop to this location or at least for the next few weeks.