Xi'an was once named Chang'an 長安 as in Eternal Peace. It was the capital of the Tang Dynasty China. As the capital moved with new dynasties, it was renamed 西安 as in "An" in the West of China

西安is a city in "western" China (really central China, if you ask me). It is the ancient capital. It used to be called 长安, Eternal Peace.

Though I have visited Xi'an, I would prefer to postpone my trip to the place of eternal rest.

Have you gone to Xi'an means you went to and is still there. 你去了西安.