2 Ljubljana Full Day Trips Too Much?

I've been only to the Škocjan not to Postojna caves. I understand the Postojna caves are more of a touristy experience, whereas the Škocjan is a little more of a guided hike. (I was not allowed to take pictures inside the caves, which was frustrating.)

It's probably easy to do Postojna by public transportation without a tour; Škocjan is probably doable too that way but might require more walking or a taxi from the bus stop; not sure, I had a car.

Lake Bled is lovely. It is also touristy, which doesn't spoil the amazing view or the experience - but some people prefer the much less developed Lake Bohinj area. You can take a pletna boat out to the island and the church (I never have). Some people hike the nearby Vintgar Gorge.

Other things to see as day trips from Ljubljana by public transportation (not that you have time for all of this, but some alternatives): the lovely towns of Škofja Loka (bus), Radovljica, near Bled (train or bus), and Kamnik (train or bus). Last time I was in town, I combined a day trip to Radovljica with Bled: train to Radovljica, bus to Bled from there.

I don't know the language, either, but I've never had an issue getting around anywhere in Slovenia. Most people speak a little English, and many are fluent. I've had more trouble in other countries. In any event, I would not let the language barrier deter you from doing self-guided tours. Lake Bled is an easy bus ride from Ljubljana, for example, and there are plenty of buses all day each way.

The populace of Slovenia is extremely well educated and English is widely spoken, especially by those under 30? 35? I speak not a word of Slovenian and even back in 2015 I don't remember having to try to speak Russian and hope they understood me (that never goes well!). Even the fellow selling tickets at the Ljubljana bus station spoke very good English.

So you don't necessarily need to limit yourself to bus tours. However, they are a convenient way to see two different sights the same day, which can be tricky to pull off via public buses and/or trains.

I'm pretty sure Postojna is still accessible by either bus or train. I've been there twice (long ago) and have never rented a car. The castle I have no clue about. There is a castle right in Ljubljana, but I've never been to Predjama and can't compare the two.

Skocjan is also doable by public transportation but probably somewhat trickier. I ended up having to walk perhaps a mile or so. That probably would have been avoidable if I had gotten an earlier start--which is more or less the story of my life.

Ljubljana is lovely, and you can certainly occupy yourself there for two days (or more), but you need not miss out on Bled if your only concern is transportation. It's easy to get there by public bus. There are two stops in Bled; the second one is near the lake. The bus driver may not necessarily speak English, but in my experience they'll spot you as a tourist and have a darn good idea where you want to go.

In 2015 it was often possible to get a seat in a van-taxi for the return. The taxis showed up at the bus station shortly before the bus was due to depart, so if you might be interested in saving a bit of time on the return trip, don't rush to buy your bus ticket. The cost in 2015 was 7 euros per person. I never spotted anyone offering a comparable service in the other direction, from Ljubljana to Bled.

I had excellent experiences every time I stopped into the Ljubljana Tourist Office to ask for information. It could be a good resource for you.

Edited to add: Since you mentioned being a senior: How is your night vision? I'm 67 and mine isn't good, and I couldn't discern color differences at Skocjan because the light level was a bit low. However, I don't know that Postojna would be any better where the colored lights are not deployed; I was decades younger when I visited Postojna.

Thank you both for your very valuable input! I hadn't even considered self-guided tours via public transportation, but since you've told me that English shouldn't be too much trouble, I'm game! From Rick's book, I know that Postojna is more touristy, but I was more interested in the Castle. Rick says there's a combo ticket for both for €36. I can save a lot of money this way! He mentions that Škocjan Caves is a bit trickier to get to via public transportation, but doable. I have his 2018 book, so I have a bit more reading and research ahead of me. I'm a pest at the TI's, so thanks for letting me know they're friendly! I'm never afraid of asking, especially since I'm travelling alone. I'll have 2 full days to explore Ljubljana and definitely plan to visit the castle. After years of travel, I still love castles and architecture, but I'm "museumed out." I plan to spend much of the other 2 days hangin' with the locals. Thank you, again! You've both been a tremendous help!

Have fun! Ljubljana is wonderful, perhaps my favorite city in Europe.