Her study houses a really huge collection of books on history, architecture, and geography of the places we have been to.

houses 在这里是动词，由名词 house（房屋）转化而来，表示"容纳、收藏"的意思。这种名词转化为动词的用法在英语中很常见，用来形象地表达"像房子一样存放物品"的概念。