Slovenia

I'm afraid I can't advise on organised tours from Ljubljana, but both Postojna Caves and Skocjan Caves are not too difficult to access from Ljubljana by public transport.

Postojna can be reached by a number of trains or buses daily, either directly to the cave (some buses) or with a short walk from the town center to the cave entrance (most other buses and all trains). Skocjan can be accessed by taking a train to Divaca, where a free shuttle can take you to the cave entrance or you can do a leisurely 45-minute walk through the countryside on a marked path. Information on which train to take to connect with the cave shuttle can be found on the following link: http://www.slo-zeleznice.si/en/passenger-transport/around-slovenia/trips-by-train/the-skocjan-caves-regional-park

Caves in Slovenia can only be seen as part of a guided tour that is run by the institutions managing the caves.

I've done both caves via public transportation, though Postojna was a long time ago. The tourist office in Ljubljana is excellent and will probably have information on the bus schedules to both places. The prevalence of English-speakers in Slovenia makes it easier than usual to manage something like this via public bus.

Postojna is a bit more developed/touristy. For example, it has some colored lights, and there's a little train thing running part of the way.

Skocjan seems to be preferred by the folks who like more natural caves. I don't think it's a clear call. I'm 65 and would have appreciated just a little more lighting at Skocjan, of whatever color. When the guide mentioned the different colors of the formations, they looked nearly the same to me with my old (and not 20/20) eyes.

Thank you both for your kind replies. Iam looking forward to our trip to Slovenia, though I probably won't follow the path of the illustrious Ms. Trump. Iam from California and our politics are quite a bit different. Hank Novato, CA