We will be in Zagreb for several days in Jan. What are some good day trips either by train or bus, we will not have a car?

Thanks Ed for the uplifting comment. It is good to know that somehow I could be of help although the thread is way old.
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What has this got to do with Zagreb day trips? Must have been posted by mistake.

We visited the baroque town of Varazdin and loved it. I don't recall the actual distance (and we had a car) but it was definitely doable as a day trip. I'll be honest; there isn't a whole lot to do there but the architecture is very nice and very different from the rest of Croatia - reminiscent of Austria or southern Germany. There is a castle that can be toured, I believe, and many shops, restaurants and cafes.
http://en.wikipedia.org/wiki/Varazdin

You could also easily visit Ljubljana, less than two hours north. We loved this small city. Again, the architecture is fantastic. You can tour the castle above the city. It's very walkable and pleasant. http://www.ljubljana.si/en/tourism/

Tracy

Hi - do you guys know if you can take a day trip to Bosnia from Zagreb? I am attending a workshop in Zagreb and my husband wants to see some things while I'm in class. Trying to see if this is possible.

I think he'd be about two hours away from the border so he could certainly visit Bosnia if that's his goal but I would check and see exactly what is in that part of Bosnia first. There's no reason to drive all the way there and not see anything of interest. Unfortunately, the two cities most worth seeing are too far away (Mostar and Sarajevo). There are some great day trips within Croatia (see the older posts above - I particularly liked Varazdin myself) but I would recommend that he visit Ljubljana, the capital of Slovenia. It is a lovely city (and Slovenia is a wonderful country) and relatively small so he could see it all in a day and then do the relatively short drive back to Zagreb.

Plitvice Lakes National Park: about a two hour bus ride each way (if he can coordinate the bus schedule). Or, he could just rent a car for the day and drive down, probably the easiest. This park is breathtakingly beautiful: full of waterfalls and huge lakes. Long hikes or short, easy hikes are possible. If he goes, tell him to get the first thing in the morning before it gets crowded.

Ljubljana is also an entirely different kind of option but a nice choice, too. I love the city. I'd probably do it by train unless he has a car. Check train schedules - there are a couple of direct daily trains per day between the two cities. There's a border check each way (on the train itself) so make sure he has his passport with him.