To our astonishment, we were in front of a small house which seemed to have been built centuries ago.

astonishment 是名词，由动词 astonish（使惊讶）加上名词后缀 -ment 构成。astonish 来自古法语 estoner，意思是"使震惊、使惊讶"。-ment 是常见的名词后缀，表示动作或状态。 astonishment 表示"惊讶、震惊"的状态或感受，通常用于表达强烈的意外或惊奇。