The Science Facility.
A heavily guarded science facility where experiments are done on humans and extraterrestrials. I have returning to The Facility for decades. On some occasions I am outside, trying to break in. Other times I am already inside and being attacked by alien escapees. And at least one time the facility was guarded by lions, and another time by dragons.
As a boy, I remember escaping through an extremely narrow vent in the ceiling which led to a large garage filled with military vehicles. Once, as I climbed the ladder to the hatch a fetus the size of my thumb grabbed my hand and bit me. I shook it off of my thumb and it fell to the ground below. Then it scampered away.