The Ventilation system is a set of pathways in the 'vent' layer that lead you from one room to another. These layers usually show up between floors. Transporting yourself through the vents is simple since it requires minimal equipment (only one Screwdriver for the least), and it can repeatedly be done in a jiffy. Many escape routes require you to use the vent system (i.e., K.A.P.O.W. Camp's "Speed McQueen"). Sometimes, vents will lead you up floors, thus, allowing you to access the roof via the vents. In The Escapists 2, some vents have Fences in them, so make sure you bring cutters if needed.
In order to get in the vents, find a vent entrance above you and get up on a desk or a Stepladder (TE1 only) / Makeshift Ladder (TE2 only). In The Escapists 2, there are also Vent Covers in the floor which you can use as an entrance. Use a screwdriver to unscrew the Vent Cover (or use cutters to cut the vent). When you're done, press the interact key to go into the vent system. Make sure to replace the Vent Cover you tampered with. If the guards see what you've done, they will send you to solitary (in The Escapists 2 it will raise the Security Level by 3 stars). Once you are in the vent system, you can unscrew another Vent Cover and get to your desired destination. If your destination room does not contain a desk or a ladder, remember to take another Stepladder/Makeshift Ladder so you can get back into the vents.
In vents, you can sometimes find Prisoner Stashes of important items left by escapees (The Escapists only). The vents are also a useful place to store contraband since guards will not search the vents normally.
One should use caution and enter vents through discreet areas. If a guard sees that the vent cover is missing or damaged, you are very likely to be sent to solitary (in Escapists 2 this will raise the Security Level by 3 stars). Any player seen within these vents will be sent to solitary.