There were a lot of hills in the park, and it was very tiring to ride a bike up, but when you got to the top and stared at the amazing view, it was worth it.

was 是动词 be 的过去式，在这里表示"是"的状态。 worth 是形容词，意思是"值得的"，表示某事物具有足够价值或重要性。 it 在这里指代前面提到的"骑车上山看风景"这件事。 was worth it 这个短语表示"（虽然付出努力）但很值得"，强调经历困难后获得回报的价值。