No, they are abandoned now (maybe used for tourist trains). There were rather small containers, 20' or similar, unfortunately I have no photos, I lost my camera due to issues with Securitate.
Interesting, that's an info not on the .net .
Do you remember where they were ? Maybe on a map ?
Thanks for the answers.
Note: I know about loading gauge, but I assume that a narrow enough track gauge would also be a limiting factor because of the unstability and risk of derailment.
At some extreme, yes, but rail cars are actually more resilient to toppling over than you might expect, especially due to the flanges on the wheels. Trains are generally not likely to tip when taking a curve - the banking of the track is more to reduce lateral loading on the tracked (and increase passenger comfort) than to prevent a rail car tipping like an overloaded truck.
I've never seen standard containers on 600mm track, but I am sure it would be workable if sensibly built and operated.
Flanges don't have anything to do with toppling, they only have to do with following the rails itself. Some steam locomotive wheels are intentionally left "blind" (without flanges) to increase turning radius (efectively turning only a handful into "bogies").
But yeah, I can see that it could be quite problematic. 600 mm would be very narrow, and I guess the structure/loading gauge would usually not allow such.