Thanks to the Man in Seat 61, my favorite rail travel website, I've discovered the cheapest way to go to visit my friend in Trier, Germany. If you book an 'any Belgian station' via Brussels Eurostar ticket (which I managed to do for £39 each way) you can get as far as Arlon. A ticket from there to Luxembourg is about £10 each way and then when you arrive at Luxembourg you buy a Luxembourg Special ticket to Trier which is just under €10. That ticket is a bargain day return between Luxembourg and Trier but is much cheaper than a single so worth it even if you're only going one way but you can only buy it at the station. Total journey time around 8 hours depending on connections. Much more relaxing than travelling by plane and probably not much longer by the time you factor in travel to and from the airport, the two-hour check-in time and the wait for the baggage at the other end.
But much as I love train travel, I have to admit that the three hour stop-start journey between Brussels and Luxembourg is somewhat wearing, particularly when it's as hot as it was when I came back yesterday. There was an apology for air-conditioning - a sort of feeble breeze coming through the vents below the window that only cooled any part of you that you could get in close proximity to it. The interior of the carriage resembled a sauna. People getting on at the various stations en-route exclaimed about the heat in a variety of languages. The first thing I did when I arrived at Brussels was buy a cold beer!