You need a grappling hook. You can purchase them from the store. There will be a slit you can look through, on the back of the bunker. The card will be on the stairs, which you can grab and pull to your with the grapple. After you get the card and open the first door, you will need a password changer for the second door at the bottom, and then you'll be inside, and can get your omega recipe.
(WARNING: Practice with the grappling hook first, if you don't know how it works yet. You could very well throw it and lose it if you don't use it correctly, and you'll have to buy another.)