Martvili Canyon's limestone walls rose from a Miocene seabed when the Caucasus mountains themselves were still forming. The Abasha River carved its fifty-metre gorge through sedimentary rock over millennia, exposing fossil-rich strata that geologists first documented in the nineteenth century. Prometheus Cave—Georgia's largest surveyed karst system—extends eleven kilometres beneath the Kumistavi hills, though only one kilometre opens to visitors. Soviet-era speleologists mapped its chambers in 1984, cataloguing stalactites that grow one centimetre per century. Today the martvili canyon & prometheus cave group tour from batumi connects two ecosystems separated by sixty kilometres of Colchian plain. Martvili's upper canyon permits rubber-boat drifts through corridors where Colchis ivy drapes limestone ledges; the lower canyon restricts access to footbridges suspended above turquoise pools fed by underground springs. Water temperature holds constant at fourteen degrees Celsius year-round. Prometheus Cave maintains its own microclimate—year-round seventeen degrees with ninety-five percent humidity—conditions that preserve its six million years of calcium carbonate deposits. Electric lighting installed in 2011 follows a looped walkway past the Medea Hall, a thirty-metre chamber named for the mythological sorceress said to have hidden the Golden Fleece in these mountains. Both sites became protected zones under Georgia's national park system in 2008. The martvili canyon & prometheus cave group tour from batumi operates Tuesday through Sunday; Monday closures allow ecological monitoring. Conservation fees—forty lari per site—fund trail maintenance and bat-population studies. Tour operators coordinate departures to stagger visitor flow, limiting boat queues at Martvili's dock. Round-trip transport from Batumi spans roughly ten hours including transit, with three hours allocated for Martvili exploration and ninety minutes inside Prometheus. The route crosses the Samegrelo region, passing tea plantations and hazelnut groves that carpet the lowlands between the Black Sea coast and the Lesser Caucasus foothills. Both attractions close from November through March when seasonal rains swell the Abasha beyond navigable levels.