On a clear day you can see up to 30 miles over the mountains in all directions. Yesterday when the President, Mrs McAleese, arrived visibility was a mere 100 metres.
The Great Wall of China, a wonder of the world, was shrouded in mist but, shielded by umbrellas, the President climbed to one of the viewing towers.
The bad weather affected the whole greater Beijing area. Mrs McAleese and her husband, Martin, viewed the faded empty splendour of the Forbidden City through a fine misty rain. Their motorcade dropped them at the main entrance, where hundreds of Chinese sightseers were held back by guards, and they progressed through the many courtyards and palaces to the garden at the far side.
The 100-hectare Forbidden City, most of it dating from the 15th century, contains 8,000 rooms and was home and administrative centre to 24 emperors.
At one time 6,000 members of the court lived there, and ordinary Chinese were forbidden to even approach the walls. When the last emperor, Pu Yi, was forced from power in 1911 it fell into disrepair and suffered bouts of looting.
Today it is an oasis of calm in a rapidly overexpanding capital city. It is so vast the highrises dominating the skyline are not visible from its interior.
After a morning viewing the imperial past the President went to the centre of current Communist power. At the Great Hall of the people on Tiananmen Square, bedecked with Irish and Chinese flags, she was officially welcomed to China by President Hu Jintao.
Shortly before her motorcade drove up two other important guests, the media mogul Rupert Murdoch and the former US president George Bush snr drove off in theirs - separately.
The weather forced the ceremony from the square, and the eyes of the hundreds of Chinese tourists observing Mao's mausoleum, into one of the vast interior halls. The 50-man military band of the People's Liberation Army played both national anthems and Mrs McAleese, escorted by President Hu, inspected a 150-strong guard of honour drawn from the army, navy and air force.
The state banquet that followed private talks between the two presidents was a lavish 10-course feast.
The talks between the two presidents covered three areas: the progress and advancement of their own countries, bilateral relations and multilateral relations taking in the EU and the UN.
Her meeting with President Hu, Mrs McAleese said, was one of the most friendly, open and wide ranging discussions she had ever had with a head of state.