Vis07: A disastrous catastrophe! You need a weapon to get out of this mess. Do you remember the scientist, who obviously tried to open a malfunctioned security door with a crowbar? You exactly need this crowbar. Try to find a way through an air duct inside the men’s restroom.
Vis08: The tunnels of the transit system are assailed and burning. There is definitely no escape. Take your way through the storage area near the elevators.
Vis11: A high explosive crate, a freight elevator and an open fire, powerful enough to break the high explosive crate. After you blast the wall you have to shut down the power engine by every trick. Now you can use the air duct on the lower level.
Vis12: The metallic bridges lead you to different storage depots. You have to open all gates in the control room in order to get to the freight elevator, which will take you much deeper in the earth. Some gates and doors are locked or malfunctioned and you need a scientist for help and some other tricks to get through it. Complete the sparking power wires of the broken button in room 1 by a metallic conducting thing: perhaps a barrel or something.
Vis17: Teleportation is not that simple to explain. Teleportation is incalculable and influence your imagination, so you will not know where you are and if you are dreaming or waking.
Vis19: The incalculable system of teleportation took you far away from the Black Mesa Central miles away from everywhere. There is a scientist, too, but he is dead. Although he will be your only chance to get out of this, because he has got a security card to open the steel doors. Further, be very quiet and with caution. Your enemy seems to be everywhere and they could call reinforcements, if they will see you.
Vis20: On the roof, there is a power generator. You have to activate all buttons in order to activate systems like lighting and security doors. But all doors are locked and there is only one way to get out of the building and on the roof. There is a small air duct in the elevator shaft. Further, you have to use a scientist for help to get through the lower levels. Above all he will open a storage room for you on the areaway, which is a weapon supply depot!