Locked bunkers have been part of Call of Duty: Warzone’s Verdansk map for a long while now. Little by little some of them were made accessible. Yet, you can't just walk in like that.
For most of the bunkers, you need a red access card, which can be found as an extremely rare drop from legendary loot boxes all over Verdansk. With this card, you can open bunkers 00, 04, 05, 06, and 09. Since the end of August, you can open three more bunkers: 01, 03, and 10. However, you do need eight-digit codes to do so. Bunker 01 can be opened with the code 97264138, bunker 03 with the code 87624851, and bunker 10 with the code 60274513. All bunkers contain lots of loot and some strong killstreaks.
You can read more on bunkers on the EarlyGame website: