I try to ride around three to five times a week. When I started, I’d leave my apartment building and ride down Chang An Avenue (长安大街) from one side of the second ring road in Jianguomen (建国门) to the other side in Fuxingmen (复兴门), and then back again. That route is not bad for a quick ride. The bike lanes are usually over 5 meters wide. It was about 16 km round trip. But not too exciting.
After some experimentation with different routes, I found that Di’Anmen Street (地安门大街) is good to ride on. The bike lane is somewhat wide and most of the buses are electric so there is less pollution. So the whole ride takes about an hour depending on traffic. I usually go counter clockwise so that my return to Jianguomen is on Changan Avenue and I can ride fast in the big bike lanes. Plus it goes past Tiananmen Square (天安门). There is almost always a crowd to look at taking pictures of the square or of the gate to the Forbidden City so people watching at stop lights can be interesting.
The pollution in Beijing is pretty bad. I get sore throats from it if I go out and ride on bad days. (Check the Beijing US Embassy website for current conditions — usually between very unhealthy and hazardous.) Once I went out during the rain, and when I got home I was black with tire particles and greasy soot that was sprayed up on me. It was scary to realize all that is normally in the air.
Sometimes when I feel like a leisurely ride, I go around the Forbidden City (故宫). The area surrounding it is dimly lit, and seeing the massive walls and grand entrances with nobody around are always impressive. Sometimes it leaves me with an eerie feeling especially after the spotlights have been turned off.