Go outside the hospital and face the main entrance.
Looking towards the doors spawn a car and the car should spawn inside the hospital.
Go inside and get into the car. The car should go invisible but its still there.
Press y and get in. When you get in all the surroundings go invisible and it looks like you are outside but you are still in the hospital.
Once you get out of the car it is still invisible but the surroundings go back to normal. Class!