Beijing has, by far, the most historic, scenic and beautiful sightseeing spots than any other city in China.
Of course there is the Great Wall, and in addition, the Forbidden City, Summer Palace, Temple of Heaven and many historic buildings, parks and places of interest. It would take about 2 weeks to see all the sights in Beijing.
The Great Wall of China
By far number 1 on your list should be the Great Wall. With thousands of years of history the wall has claimed thousands of lives and is one of the greatest achievements of man-kind.
We recommend visiting the non-tourist section of the wall at Mutianyu. It takes longer to get there (it's about 45km out of Beijing) but it's well worth avoiding the crowds at Badaling.
No. 6 Tourist Bus
Xuan Wu Men - NE corner of intersection
Dong Si She Tiao - NW subway entrance
An Ding men - SW subway entrance
Private tour: from RMB 1,500 for the day, includes guide, driver and transportation in private car
Admission: RMB 35
Opening hours: 7:30 a.m. - 5:30 p,m.
Recommended time for visit: allow 2-3 hours + Travel time
Best time to visit: Autumn for changing foliage and best chances of clear views
The Forbidden City
Located in the Center of Beijing, The Forbidden city was the palace of China's emperors for thousands of years. The entire mini-city is built in traditional Chinese architechture and is a fascinating day-trip we highly recommed. There are usually a lot of people going here though.
Address: Dongcheng District ???????4?
Phone: (010) 65132255
Hours: Open daily, 8:30am to 4:30pm
Directions: Subway Line 2 - Tian An Men East Station