Flying from Las Vegas US to Bangkok through Beijing where I can go with 144 hours visa?

Following my previous question. I have 15.5 hours layover coming from US and 18 hours on my way back 3 months later. I plan to take 3 day stopover on my way back and maybe 4 days stopover on my way from US. Since I cannot go to Shandong province, where I can go? Can I take some tours to Great Wall and around BJ?