I haven't been, but the station at Nova Gorica is in Slovenia, but the forecourt is in Italy.
Whereas once it had armed border fences, now within Schengen there are apparently no obstacles any more.
As 30907 says, not quite - from memory, the border line is about 10 - 12 metres from the station door. Still quite amazing though, I agree.
And it hasn't been 'armed' especially (apart from the fact that police both sides routinely carry side arms) for many years. Yes, I think it was a tense border in the early-mid 50s, especially after the UN (I think it was) first delineated it, but even by the 80s, my impression is that it had become quite friendly. There was actually some border revision (in the 70s, perhaps?) because the line zig-zagged eg inside a cemetery, which kind of made putting flowers on some grave a rather special experience
Italy allowed a corridor road to be built through the cut off north of Gorica to what is now Slovenia's Goriska Brda region - not sure when, but I think it was still Yugoslav times, ie pre 1991.
By the early 2000s, ie before Schengen, the border fencing was removed in front of Nova Gorica station, and the public was allowed to enter the Italian side, but not beyond the bounds of the square. Whether anyone actually controlled it from the offical border crossing - about 150 metres down the road - I have no idea.
Meanwhile all the usual border apparatus has sprung up between the states of the former Yugoslavia....
Well, the Croatia - Slovene border is a Schengen border, so it's actually very much mandated by the EU. I suspect the locals know how and where to do a quick cross for a glass of vino in better a gostilna. But I did get told of a group of four Germans who strayed into Croatia from Slovenia not too far from Ljutomer who were fined something awful - I think it was euro 400 each by the Croat border guards, which seems a trifle excessive. (But I suppose Croats away from the coast have to make their money somehow
) This was maybe 7 years ago.
As for, say, Bosnia to Croatia, or Montenegro to Kosovo etc, I suspect there are many places where the locals cross illicitly. Pretty much impossible to seal those borders completely without huge amounts of money.