There are a whole slew of new achievements to be found in the zombie map ‘Mob of the dead’ of Black Ops 2. One of these achievements is called Paranormal Progress. This achievement can be unlocked at any time and is really very simple.
The requirements of the achievement are as follows; simply open a door in the facility, without paying for it. It’s that easy. There are an uncountable number of doors in the prison you can open by zapping a wall panel in ghost mode, but I decided to use this one:
When you are at the door that leads to the roof (next to the glass case containing the Control Valve), move back through the corridor that leads to the infirmary in ghost mode and search the adjoining rooms for a portal. Enter through the portal, turn right, and leap up through the ceiling to access the roof. Now head to the nearby doorway and zap the panel to open it.
And hey presto, you’ve unlocked the achievement.