I'll second you on this one: travelled on this line (including a trip on the mentioned Trois Vallees preserved line) during a tour of the south of Belgium a couple of decades back. I would reckon this corner of the country around Philippeville / Couvin (in a sort of "bulge" of Belgium protruding into France) as the most scenically atttractive part of Belgium, that I've seen -- more so to my taste, than the Ardennes a bit further east. (Belgium's north has plenty of interesting features; but for me at any rate, scenery is not one of them !)
Have come across many accounts of this line, with its interesting hopping between the two countries -- haven't visited those parts myself. It would appear that not everyone who's done so, has found the area in general -- railway matters aside -- an unalloyed delight. I recall reading an account of his travels, by a chap who ranged far and wide in Poland in the mid / late 1980s in search of surviving PKP everyday steam action. He was in this far south-eastern corner of Poland -- back then, there was a passenger service (long defunct, as of now) on the offshoot of the Goerlitz -- Zittau line running to Bogatynia, middle of this funny "panhandle" bit of Poland squeezed between Germany and the Czech Republic. He travelled on a train doing this run, originating I think at Luban: this working was steam, unlike the then diesel-hauled majority of trains on that route. Certainly in those times, it was widely known that decades of Soviet domination and general misrule had caused widespread quite horrendous environmental damage in Poland: our traveller found this corner of the country, an extreme case of same: obviously-dead rivers, dead or dying forests, large-scale industrial "muck and mess" everywhere -- except for (or in spite of) the steam haulage, he found his journey to Bogatynia and back, an extremely depressing one. (Perhaps in the post-Communist era, things in this sphere have improved..?)
