Question

at the thought在这里是什么成分？

It is true that during their explorations they often faced difficulties and dangers of the most perilous nature, equipped in a manner which would make a modern climber shudder at the thought

Answer 1

at the thougt (一想到这）在定语从句 which would make ... at the thought 当中作状语。
【形式主语It】 【表语is true】 【主语从句that （状语during their explorations） （主语they） （谓语often faced） （宾语difficulties and dangers） （介词短语作定语of the most perilous nature）, （过去分词短语作定语equipped in a manner <定语从句which would make a modern climber shudder at the thought>）】
翻译：
的确，在他们的探险中，经常会面对最险恶的困难和危险，其情形使得现代登山者一想到就打冷战。