Back 4 Blood

The fastest way to load hives (and start with a good amount of cards) is to run the first level of act 3, as it has more potential spawn points for hives than the first mission. It’s completely random for which hive you’ll get, and if you don’t get a spawn you can just back out to the camp area and try again. However, this can be done on the easiest difficulty. You do not need to own the DLC to unlock this, just play with someone who does.

Here is the location of the secret in 300 Below, courtesy of GDP Duncan.