Back 4 Blood will have you running all over the place, helping survivors trapped in goo and fetching supplies and all that, but you should do some exploring on your own. Not only will it lead you to find important items to help you survive, but you might come across one of the game’s secrets. In Act 1, Book Worms, there is one that is easy to miss if you don’t check around corners. Here is the Search & Rescue secret in Back 4 Blood that will earn you the Bell Hop achievement or trophy.
At the beginning of Book Worms, you will be fortifying a library. Complete that task, and you will be directed to find and help the survivors at the Haven apartments. When you get there, shoot the propane tanks down the stairs to blow a way into the apartment. A horde will come down on you, so focus on them and any Sleeper pods you see on the walls in the basement.
The secret is close now. Upon entering the basement, turn left to find some stairs. Go up them and get through the door on the left. To keep going up the apartment, you need to go right, but instead, turn left, and you will see a desk in the corner. Go behind it, and you will find the golden skull trophy, which is our secret. Interact with it to get the in-game Accomplishment, and the achievement or trophy will pop.