Dying Light has its own loot cave… except there’s way more cave and not a whole lot of loot. It’s really just a way to poke fun at Destiny .
In the top right of the map in Dying Light , you can dive into a pool that will lead you to an underwater cave. When you surface, you will notice a group of zombies and you get a message saying “your destiny is to build your legend (and get loot).” Then the zombies rush you. If you manage to clear the whole cave you will get another message saying “Enough! Patch 1.0.2 has been released! Do more quests.”
To see how to reach the small easter egg, check out this video from VGFAQ.
Source: VGFAQ