介词后宾语从句

上海2019年高考考试题目：

Nature is full of wonders. In 【 】 is one of the most breathtaking sights in nature, millions of baby Ridley turtles broke out of their eggshells under the sand at one of their mass nesting grounds in coastal Orissa.

这一空中答案是what，分析只说了是介词后的宾语从句，但仍然不太理解，有老师能帮忙剖析一下这句话的句子成分，具体解说一下介词后的宾语从句吗？

that从句不能作介词的宾语。但疑问词引导的疑问分句与融合型关系代词引导的名词性关系分句是可以作介词宾语的。这里用what就是引导名词性关系分句。what=the thing which, 其中the thing可以参考语境改用其他名词，在这个句子中what=the sight which. sight的意思是a famous or interesting place in an area 。in what is one of the most breathtaking sights in nature = in the sight which is one of the most breathtaking sights in nature. 这个介词短语在句子中作地址状语。