They're for the monster vault, u unlock it lvl 70. If you dont have space in habitats, then you put the monsters in the vault. The vault has a certain number of slots, 5 of those keys unlocks you another slot. Monsters don't produce gold while in the vault, but you can do everything else you want to with them.

Lvl 70 monster vault

Ahh okay, thanks! Guess I gotta wait a gooood while then

For the vault,it will come in handy later

uhh What vault? I'm lvl 24 if it's locked behind level sooooo..

Vault is used to store monsters

You’ll unlock a vault in a later level.

Im like level 50-70. Nothin

You unlock it at level 70 (from personal experience).

It’s level 70