The dramatically situated Drapsang Monastery is a worthy detour off the main highway. Nuns will show you a skull-shaped rock and statues of Guru Rinpoche and his emanations in the main chapel. The guru meditated in a cave 10 minutes' walk away on a cliff-side trail. The path then continues for an hour on a fine kora around the back of the hillside, up to a hilltop chapel and then down past former monastery ruins, making for a fine walk.
Drapsang is a 4km drive off the main road, turning at around Km2062, 15km from Kajar. Pass the lower Nyingma school monastery and then persuade your driver to take the crazy switchback road up to a car park at 4860m. From here it's a 10-minute walk away.