We read about this "mini train" in our guidebook and then went to the Place de la Constitution looking for train tracks. We didn’t find them, but we did find a small stand with Pétrusse Express stamped on it. We managed to buy our tickets for a tour about 45 minutes later. I was still looking for train tracks in the Pétrusse valley, where the tour was to take place. As a result, I felt at least a bit cheated (and like a complete idiot) when the "mini train" pulled up — it looks like a train, sure, but its just a glorified, train-shaped bus with three separate "carriages."
The tour itself was okay. In each car on the "train" there were about 6 rows of bench seats for three people each. Above each was a built-in console with a set of headphones hanging down, and buttons with flags of several countries, indicating the relevant languages for the recorded commentary, reenacting various historical events of the city. There was at least English, Spanish, French, German, Italian, Luxembourgish, Dutch, I think Swedish, and a couple of others. The journey lasts about an hour and involves riding through the Petrusse valley, where the views of the river and of the city’s fortifications are excellent.
There were several problems, though these were actually a source of great amusement to my friend and me. We got situated in our seats and put our headphones on, and soon the "train" started moving. The commentary began...and so did the problems. First, and this was isolated, my English button didn’t work. All the other languages seemed to, but not English. So I settled on Spanish, as it had only been a couple of months since I’d returned from 5 months studying in Mexico. This was okay, as I could make out the majority if I concentrated really hard. But then the other problem (the funny one) was that every time—and I mean, every single friggin’ time—we rolled over anything resembling a bump, the commentary would revert to what I think was Luxembourgish, though I suppose it could have been another Germanic language (not English, unfortunately). So, after every such bump, you could see every person in the "train" reach up to press the button of their preferred language. It was like synchronized swimming, just without water and in a bus that looks kinda like a train.
In all honesty, I don’t know if this tour was good or bad. It was clearly a quick way to get down and around the valley. But as I never heard the English commentary, I can’t speak for it personally, though my Scottish friend I was traveling with told me she had some difficulty making out everything it was saying, because it was so dramatized. I can vouch for the dramatic touches on the Spanish version, though. Little gems like, "¡¡Dios mio!! Juan, JUAN, ¡fuego fuego! ¡ ¡AAAAAARRRRGGGGHHHH!!" stand particularly out in my memory.