Eleven kilometres past Khertvisi Fortress towards Vardzia, atop a high rocky hill across the river (which flows far below in a gorge), the remains of the once near-impregnable Tmogvi Castle date back at least a millennium. You can walk to it in an hour or so (4km) up the west side of the valley from Vardzia – and continue north to Khertvisi, on off-road trails most of the way, if you want.