You can visit Tianjin and Qinhuangdao. They can be reached from Beijing by bullet trains. Wear T shirt and take a jacket, because it will be a bit cold at night. It is windy in Beijing, jacket can be light but can keep you warm enough. I caught a cold when I visit Beijing in April. It is still 27 or 27 degrees at daytime in early October, but will cool down in the evening.

I believe Cheng De is a better place to visit. It is not too cold in early Oct. though jacket/sweater is needed.

Thanks for the info. Very helpful.

you will be beijing in october ,so bring jacket is enough,