Translation:If you come to Beijing, you must go to the Forbidden City.
It's not exactly the same thing. 故宫 (short for 故宫博物院) means 'palace museum'. There's one in Beijing, in the Forbidden City, and there's another (also called gugong) in Taipei, where most of the treasures of the original palace museum reside, which were evacuated along with Chiang Kai-shek and the Kuomingtang in 1949. According to Pleco, 'Forbidden City' should be 紫禁城 (zi3jin2cheng4), which refers specifically to the palace of the Ming and Qing dynasties in the centre of Beijing. Incidentally, both 故宫 are well worth visiting, the Forbidden City for its architecture and the National Museum in Taipei for its unparalleled collection of the treasures of ancient China.