We went to Prometheus Cave from Batumi in July. The drive is long, about three hours, but it's worth it. Inside there are huge halls, illuminated stalactites and stalagmites, and classical music playing — the atmosphere is truly magical. The temperature is around 14 degrees, so after the summer heat it feels great, but bringing a jacket is a good idea. The groups are large and it's hard to hear the guide, so it's better to hang back and walk at your own pace. At the end of the route you can take a boat ride on the underground river for an extra fee — short but impressive. The only downside is the slippery steps, so watch your footing, and don't wear light-colored shoes. I'd recommend it, but keep in mind the crowds and the long drive.