Mercy Hospital was a medical facility on Earth, located in the Mission District of San Francisco, California. This was a seven story building with levels connected by elevators and stairs.
On the first floor, there was a nurses station, gender segregated bathrooms, and a fire hose. On the second floor, there was an operating theater.
In 1986, Pavel Chekov was taken there when he was injured aboard the US Navy aircraft carrier USS Enterprise. (Star Trek IV: The Voyage Home)