unique 是修饰 concentration 的,罕见的不是遗址,而是不同特点集中于一地。
Angkor was the center of the KhmerKingdom. With impressive monuments, several different ancient urban plans and large water reservoirs, the site is a unique concentration of features testifying to an exceptional civilization.
这里的 a unique concentration of 应该译成“罕见的遗址聚集地”还是“罕见遗址的聚集地”?