If you're planning a bit of sightseeing head to Old Pine Trees of Jietai Temple— just one of the monuments located 16 mi (25.7 km) from the center of Beijing.
If you like quiet time surrounded by flowers and greenery, hang out at Beigong Forest Park in Fengtai. Want to stretch your legs some more? Head to Beijing Garden Expo Park and Museum of Chinese Gardens and Landscape Architecture, both nearby.
Fangshan Wangfotang Hua Tower is 17.4 mi (28 km) from central Mentougou, why not stop by during your stay. If you'd also like to explore some of the parks in Mentougou, Beigong Forest Park and Fahai Temple are both nearby.