When we arrived at the Riverside Lodge I was horrified to find out that there were no ramps in the building.

horrified 是动词 horrify 的过去分词形式，horrify 由词根 horror（恐怖、惊骇）加上动词后缀 -ify 构成，意思是"使惊恐、使震惊"。在这里 horrified 表示"感到震惊的"状态。