Is there a downside to basing on the Slovenian coast?

Hi.

No way can you see all that in 5 nights, IMHO.

I think I would pick two places, only, and do those. Maybe Llubljana and Piran, if you are determined on a seaside stop. You could catch the castle or a cave on the way to or back.

Lake Bled could be done as a day trip from Llubjana, but you would be pushing it, IMHO.

I don't know if Rick Steves still recommends Max's in Piran, but even if he does, I would avoid it. After confirming our reservations directly with Max the night before, we showed up only to find the place closed, without any warning or explanation left for us (apparently we were the only ones staying there, and Max decided he couldn't be bothered opening the place just for one couple, and so just completely hung us out to dry). It's the only bad experience I have ever had with a Rick Steves recommended lodging.

You can use ViaMichelin to get estimated driving times. To get from Piran to Bled you'll have to drive right past Ljubljana, which is a really, really nice city. The Piran-Bled drive is estimated at 2 hr. 20 min. each way. Although there's not all that much to do at Lake Bled and I can't honestly say that such a long drive doesn't give you enough time there, 4 hr. 40 min. is a long time to spend in a car in one day.

Driving time to the Julian Alps would depend on your specific destination there. ViaMichelin is estimating 3 hr. 47 min. to the main town on Lake Bohinj, which puts it clearly way beyond day-tripping range, at least for me.

I would be extremely surprised if the water's warm enough in Piran for swimming in May, so it wouldn't be the place I'd choose to stay for 5 nights if I wanted to visit places so far away. I'd choose Ljubljana in a heartbeat if I had to have just one base. Otherwise, maybe 3 nights in Ljubljana and 2 on the road. But I like cities with things to do rather than multiple nights in a small town (pop. 4000 in the case of Piran). I've been to Piran, but it was a very long time ago and I don't remember anything except that it was an attractive place.

It seems to me Piran would be a more logical base if you wanted to travel around Istria, but I don't know whether you'd have to expect slow-ups at the border. I'd think not since it's (as far as I know) not yet swimming season.

I hope Dejan notices this thread and responds.

At first glance, I'd be inclined to spend a couple of nights in Ljubljana, followed by a drive through the Julian Alps to the coast, where you can spend the remainder of your time. It doesn't have to be Piran, Izola is lovely and feels more like a real town and there are many lovely villages in the hinterland just minutes from the coast, too. Just know that an itinerary like this will give you very little time in the Alps, which are not feasible as day trips from the coast IMHO (on the other hand, Predjama Castle and the caves are feasible). Doing many day trips on such a short trip would make little sense if you are looking for a seaside holiday anyway.

What are your interests for this trip? Just seeing the main sights, exploring natural sights, lazing on the beach, doing some activities like swimming or cycling along the coast, gastronomy, something else? Mid-May is not perfect for a seaside holiday but not a bad time either, just not for one that involves swimming in the sea. The long-term average temperature of the sea in May is about 17 °C, although it has been increasing in recent years to about 20 °C. Still far from the balmy 24 °C in summer but manageable if you're used to cold ocean water.

Given the short amount of time I would try to be as efficient as possible with regards to where you stay and the amount of driving you do. In addition to your interests, things that will influence your itinerary include which airport you are flying into, where you are meeting up with your daughter and her boyfriend, does your trip begin in earnest in the morning, afternoon or evening, when you have to be at your departure point, etc. The first day will likely be lost to jet lag but if you are meeting with your daughter at Ljubljana Airport in the morning, you could spend the day and first night at Lake Bled relaxing and then depart to Piran through the Julian Alps, finishing in Ljubljana. If you are meeting up in Ljubljana, then stay there. If you're flying into Venice or Trieste, it might make more sense to begin in Piran. The same logic applies to your final night. If you have an early morning departure out of Ljubljana, it makes more sense to spend your final night in Ljubljana or around Lake Bled than in Piran etc.

Wow, that's all super helpful. I need to do more research and study some maps. I originally planned to stay in Ljubljana, where we fly into, but I wasn't finding any accommodation that I liked. I did find nice places on the coast, and I know half of our group would prefer to stay there. Definitely more out of the way though. I just can't imagine coming to Slovenia and not seeing Lake Bled.

Off to do more thinking, but I'm sure I'll be back.