Where is the keycard in GTA?

Hey there, I'm curious about something in GTA - can you help me out? I've been searching high and low for this elusive keycard, but I can't seem to find it anywhere. Do you know where exactly it is located in the game? I've heard rumors that it's hidden in a secret room or something, but I'm not sure where to even start looking. Any tips or hints would be greatly appreciated! Thanks in advance for your help.