The Triangle hike is in Beijing's Changping District, and is a great countryside stroll that passes small villages, reservoirs, orchards, and an old pine that marks the spot where a temple was once located. During the winter most of the people that live in the area stay inside as there's not much fieldwork to be done. We only saw a few people all day - a few out collecting firewood, and a couple using the village grindstone to grind up some beans.
Near the end of the hike we got a bit of a surprise: since our last visit (July 2009), the river had been dug up and re-routed, the landscape completely changed. Next time we visit we'll have to find a better way to finish the hike!
Statistics: 3.5 hours in total, with 2.5 hours of walking at approx. 3km/h over approx. 12km; starting height 329m, highest point 452m (at the big pine tree). Estimated 1,194kCal burned.