Transportation in more remote areas of Eastern Europe. Serbia, Bosnia, Croatia, [closed]

This summer I will be traveling through a couple of East European countries from Romania to Serbia, Bosnia, Croatia and on and I would like to visit some of the natural sights that these countries have to offer. As I don't have a drivers license (could rent a moped though) I am entirely dependent on public transport.

While planning my trip, I find that some of the places I would like to visit (see below) are rather hard to get to. I've looked at websites like rome2rio and getbybus that have proven very helpful but it appears that getting to some of these places, if only the last couple of miles, is only possible by car.

Could anyone tell me what means of transportation I have besides the aforementioned, whether it is easy to get a taxi in the more rural areas of the countries below or, otherwise give me some tips on how to explore these beautiful countries without being able to rent or drive a car? Thanks.

Places we would like to visit that are or seem harder to reach

1. Ceremosnja Cave, Serbia
2. Krupaj Springs, Serbia
3. Kravica, Bosnia
4. Vrelo Bune, Bosnia