Since you're on a business trip I'm sure you will base in Lux City, but if you have a some extra time, I'd recommend a few nights in Ettelbruck.
Ettelbruck is a lovely little town which is also a transportation hub for all trains & buses, which are free now. We stayed in Diekirch (another lovely little town) but every train or bus we took changed in Ettelbruck so we spent lots of time wandering here. There's a great little piazza near a cathedral, with outdoor tables. And a farmer's market on Friday. And a Patton museum.
If you have any interest in WWII, the WWII museum in Diekirch was fascinating. After the Battle of the Bulge, local farmers cleared their fields of military equipment & artifacts left behind — tanks, uniforms, guns, whatever. Initially stored in barns, they aggregated it all in Diekirch, in a sprawling building. You can rent an audio guide or just wander.
The castle at Vianden is worth seeing. Also there’s a chateau in Clervaux where the famous Family of Man photo exhibit (which toured the world) is now on permanent exhibit.