Stephen,
Man, Croatia is on my bucket list for places to visit - fantastic nature and really fascinating culture, but you know all this!
The plant in your pic is a "beardless iris" (subgenus Limniris) and since you found it on the Balkan Peninsula it probably is I. sintenisii. It could also be I. graminea, but I'm not sure that species grows that far south.
If you want a great reference site for many bulbous and rhizomatious plants check out the Pacific Bulb Society's website. It is a fountain of information and can at least get you on the right path most of the time.