Observatories are institutions that are actively engaged in volcano surveillance and, in most cases, are responsible for warning authorities and the public about hazardous volcanic unrest.
This is a helicopter view of the Hawaiian Volcano Observatory (HVO), perched on the rim of Kilauea caldera. It was established in 1912 (at a slightly different location) by Dr. Thomas Jaggar of MIT. The modern observatory was renovated in 1987, and a fine museum named for Dr. Jaggar was included as part of the renovation. As you can see the observatory has an excellent view of the Kilauea summit caldera, including Halema'uma'u, the home of Pele.
The World Organization for Volcano Observatories (WOVO) has more information about the necessity and location of volcano observatories.