It's indeed a normal park to tourists, not as significant as the Summer Palace and so on, so it's not a top option for first comers. But if you are local or expats in Beijing, it's a good retreat in the free time.
The place was one of the corner towers on the ancient city wall of Beijing, astronomous apparatus was created in the Qing Dynasty from the 18th's Century.
They serve set menu only now, more expensive than it was. The menu starts from 500yuan/pp to thousands yuan per person. I went there with my clients recently and they ordered the most expensive set and enjoyed it for the whole afternoon.
It's one of the three national leaders in the world whose body was preserved. The mauselium is on the south end of Tian'an men Square, people who wait to see him form a line of a mile long. It opens only in the morning.
An Arabic restaurant located near Sanlitun and east third ring road, a good option for Arabians and other muslims. Their barbeque is different from Chinese ones, as they keep mostly the flavor of the ingrediant rather than putting lots of condiment.
Beijing was ever ruled by Mongolians as the capital of Yuan Dynasty, who like Barbeque very much due to their nature of staying on the grassland, raise livestocks and cook them as food. Barbeque always tastes good because of the flavor of meat and the way of cooking.
Beijing is a landlocked city, so it's always refreshing to see big area of water, the reservoir looks like a huge lake located near the Ming Tombs area, that's why it was name after it.