Jinshanling Great Wall, near the town of Gubeikou, has been thoroughly restored, but it's distant enough from Beijing that it sees far fewer tourists than the likes of Mutianyu. That means fewer people to interrupt your hike along a steep section of Wall that winds through stunning and remote mountainous terrain. Jinshanling is also the finish (or the start) of an adventurous 6½-hour hike from Gubeikou.
Jinshanling has some unusual features such as barrier walls (walls within the Wall), a particularly high density of watchtowers, thousands of bricks inscribed with maker's marks and the year 1578, and standout towers such as the Storehouse Tower (库房楼, Kùfáng Lóu) and the Big Jinshan Tower (大金山楼, Dà Jīnshān Lóu) with its upper storey and brick stairway.
In the Small Pot Tower (小虎楼, Xiǎohǔ Lóu), there is an elaborately carved Screen Wall depicting a mythical qilin (a unicorn-type beast).
Info boards in English at various points cover history and architecture. You can hike (in either direction) on the restored section of the Wall here up to a total of about 6km. A cable car by the ticket office saves a trudge up to the battlements.
Between April 1 and November 15, direct buses (¥32, two hours) depart from Dongzhimen Transport Hub to the Jinshanling ticket office. There are two buses a day, departing at 7.40am and 8.20am, and returning back to Beijing at 3.30pm and 4pm. If you can't find the bus, ask around for the Jīnshānlǐng Chángchéng lǚyóu bānchē (金山岭长城旅游班车).