PRINCE GONG MANSION
The Prince Gong Mansion (aka Prince Kung Mansion) is one of the most beautiful and best-preserved imperial mansions in Beijing. It dates back to the XVIII century and was built for a high ranking court official. It's a lovely complex of buildings and gardens where you can spin the buddhist prayer tables, learn the happiness character and write a wish on red wish tables.
The nicest thing about this place is that it is not super crowded. It is one of those tourist sites that you visit only if you have enough time. It is definitively tailored for local tourists, so avoid any Chinese national holidays as the place will be packed. Because it is a smaller version of the Forbidden city you can take your time in observing the architecture tips that you have already learned from your guide books, like the importance of number nine (9), the importance of doorsteps, praying wheels, etc. The downside however is that there are very few English signs, so you kind of end up wandering around, admiring the garden, but not really learning anything about the mansion or the Prince.