The beautiful Truso valley, source of the Tergi River, heads west off the Georgian Military Hwy 17km south of Stepantsminda. It's dotted with ancient towers, abandoned Ossetian villages and strange mineral phenomena, notably the Abano mineral lake that bubbles with carbon dioxide. Take your passport: the South Ossetia boundary is close so there are Georgian soldiers in the valley. You are not able to go beyond Zakagori Fortress, some 18km up the valley, without a permit.
A return taxi from Stepantsminda (including waiting time while you explore) costs about 100 GEL to Kvemo Okrokana, 4km up the valley, or 150 GEL to Ketrisi. Both Mountain Freaks and Mountain Travel Agency in Stepantsminda organise buses to drop off and collect walkers who want to do a day hike in the valley. Book ahead for these services as they are often sold out.