Hawkins National Laboratory (gate)
Hopper drives up to the front gate of the lab and asks to search the premises for Will in episode 1x03 “Chapter Three: Holly, Jolly”. Nancy and Jonathan arrive at the front gate only to find it deserted with the power out in episode 2x08 “Chapter Eight: The Mind Flayer”. Murray Bauman waves at the military convoy leaving after condemning the lab in episode 2x09 “Chapter Nine: The Gate”.
Source: Filming Locations Map