Warehouses are multiple locations in Elysian Island that can be robbed.

These warehouses can be found on the map with an orange dollar case icon:

Go to the checkpoint inside the warehouse and type /robbery to begin robbing. You will have 12 minutes to locate as many crates as possible, deliver them to your vehicle and get to the hideout. It is not mandatory to steal all the crates, but the more you get, the bigger the reward. 

When you're done delivering crates to your vehicle, get in it and run away to the hideout.

Once you arrive at the hideout, the robbery will be complete. You will receive a decent bonus if you managed to rob all the crates.

Arriving at the hideout without cops near you will decrease your wanted level.