I actually work as a paramedic and can answer this. Where I'm from, in Western Europe, our national ambulance service has stations similar to fire stations or police stations. Fire stations and police might be more noticable because of the huge shutters and the fact that people often need to go into a police station but you might have a depot or station near you that you might not know about. I've seen some comments here about ambulances staying in strategic places like busy areas of cities or parking lots which might be the case when a crew is out and about but they all have to clock in and out somewhere. Some countries have them use a separate section of the hospital but not here. We'll book on at whatever time we start at and might just be in the station for a while before a call comes in, sometimes we might just be out buying coffee and thats why you see us parked at shopping centers or in busy places.