Complex sentence: Part of Angkor Wat has been shown to hold one half of the triangle of light in a hidden temple room; the site is, in reality, a temple complex dated back to the Angkorian period (9th to 15th century).
Split into simpler sentences: Part of Angkor Wat has been shown to hold one half of the triangle of light in a hidden temple room. Really this site is a temple complex that comes from the Angkorian period (9th to 15th century).