Angkor, between Ta Keo and Angkor Thom
The small shrine was originally associated with a now-vanished hospital (built in wood) of Jayavarman VII. The king built four such hospitals around Angkor Thom, and 102 in total throughout his empire. It is located 150m (500') due west of Ta Keo, halfway between Ta Keo and the Victory Gate of Angkor Thom. The rear of the chapel (the west face) is seen here.
There is another, very similar, chapel just outside the west entrance of Angkor Wat.