Best of the Adriatic - extra nights in Ljubljana ...

https://www.slovenia-explorer.com/

I did the cave and castle tour. Small group in van with guide. The pickup point was about one block from the hotel. Very convenient and goes places you won’t see on RS tour.

I agree with the suggestion Carol mentioned. I did that half-day tour at her recommendation, and I especially loved the cave tour! The RS guidebook says not to bother going inside the castle, but I did it anyway and enjoyed it. There’s a nice viewpoint to climb high through the inside back of the castle.

The addition I will suggest is that the tour also has a full-day tour, so half of the small group was going to Lake Bled after they let some of us off in Ljubljana. I really enjoyed the RS tour time in Lake Bled, and it would have been nice to not have to choose between taking the pletna boat out to the island, or having time to walk around the lake. So, I would suggest taking the full-day tour with this tour group. Then do the other option at Lake Bled during the RS tour time. ….or just enjoy the gorgeous scenery there!

If your first full RS tour day in Ljubljana is a Sunday, and you’re not going on the city walk, I would be heading to the church (the dark pink one) for their service. I ran to catch the end of it when our city walk was finished and caught the last 15 minutes. The priest’s voice was so beautiful, and the church is lovely inside!

Check out music concert options, too.

I'm not sure if you mean you have been to Ljubljana last year on the same tour(?) or that you will skip the first day of tour since you will already have been in Ljubljana a few days?
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In any case, it's easy to visit places on your own by public transportation if you want to branch out and do things on your own. Slovenia does not have a big train network, but there is a good bus system.

One of my favorite little towns in Slovenia is Skofja Loka. It's about a 30 minute bus ride each way from Ljubljana. You can do a little hiking near the town. If want to do some serious hiking, you could take the bus up to Vintgar Gorge and hike there. Most people hike the gorge and return out the same entrance...but apparently it's possible to exit at the other side and hike on to the little town of Vintgar and take the train from there back to Ljubljana. You could also take the bus out to Lake Bohinj, which is a much bigger area (and less developed) than Lake Bled - more of a natural area, lots of hiking opportunities there, too. Beautiful lake. The bus stops in Bled I think - a bit further on to Bohinj. I imagine you could take an organized day tour there instead.

I traveled solo through Slovenia for 25 days in 2019. Here are some things I did. You can see if any sound of interest to you.

History: The National Museum of Contemporary History in Ljubljana. The history of Slovenia from 1900 to today. I found it to be a very interesting and engaging museum. It helped me understand the story of Yugoslavia. The special exhibits can be quite good, too. https://www.muzej-nz.si/en/

History & Architecture: The Plečnik House in Ljubljana. The home of Jože Plečnik, Slovenia's finest architect whose work to some degree makes Ljubljana what it is. It's really cool to see his house -- even the furniture is creative, including a wooden chair that resembles a self-portrait. Not photography, but very interesting to the creative mind. https://mgml.si/en/plecnik-house/

Outdoors: Wander Tivoli Park.

Outdoors: Caves, as mentioned above, are worthwhile. I'm partial to Škocjan Caves over Postjana because the former is more nature and less "attraction." There is an enormous cavern there that made me feel like I was in a Lord of the Rings movie. It took everything within me not to slam something into the ground and say, "You shall not pass!" Slovenia Explorer packages it with a trip to Piran. I imagine that would be a long day (10 hours, actually), but look up pictures of Predjama Castle and Piran -- see which one speaks more to your inner photographer.

Outdoors: Šmarna Gora. A tall hill outside Ljubljana wear the locals go to hike on the weekend. I did it on a weekend and enjoyed some food from the food stand at the top. There's a church up there, too! https://www.smarnagora.com/index_en.php

It's a little pricy, but you can do the Šmarna Gora hike with a guide from Lubljana Guides, a company that is committed to trying to give visitors a true local experience. I went with Alenka. who brought along her partner Gasper. It was great! I learned so much about Slovene life. They invited me to go biking with them later during my visit -- as a friend, not as a client. https://www.ljubljanaguides.com/

Day trip (off the beaten path): Kranj. Kranj has a nice old town (admittedly, not as nice as Skofja Loka), but it also has a canyon that contains the Kokra River running through the middle of town that can be walked. It has the former home (now small museum) of France Prešeren (the Slovenian "national poet" whose verse provides the lyrics for the national anthem). It has a castle with a museum. It has a Plečnik arcade and fountain. It has tunnels under the town built by the Germans during WWII to provide safety for the towns workers in the event of bombing (never happened) -- the TI offers tours. https://www.visitkranj.com/en/

Day Trip: Radovljica. Another cute town with much to see, including a bee museum. https://www.radolca.si/en

Day trip: If you happen to be lucky enough that your dates allow it, go to the Cows Ball in Bohinj. It's one of my favorite travel activities of all time. https://tdbohinj.si/en/events/cows-ball/