I usually hit up a Mcdonald's once or twice on each trip to Europe. It's hard to beat the convenience, and as others have noted the food is a bit different. I also enjoy seeing the different architectural styles of their restaurants abroad and visited the very location noted by the op in Luzern in the summer of 2019. Memorable was the fry sauce and beautiful pastries at the cafe.
Here's a couple of my favorites so far based solely on aesthetics:
Burges Belgium on Steenstraat - the food outlet is nestled into an old Belgian gabled brick facade with ornate stonework and elaborate floor to ceiling windows. The facade is lovely complete with an iron rail, stone entry steps, and large doors. The seating area is on several floors with the top under the old timber-framed roof. Nothing like having a batch of fresh fries under a canopy of old timbers. It's worth the climb up (you have to go up to get to the restrooms anyway).
Freiburg im Breisgau, Germany on Kaiser-Joseph-Strasse - this location is adjacent to the medieval gate tower Martinstor. It tries to blend into the old structure with its monochrome muted brownish signage and arched covered entry. If one is just enjoying the lovely architecture and avoiding falling into the Bächle they might not even notice this little burger spot. But since you'll want to see the old tower, might as well relieve your bladder and get some refreshments where you're there. Then head up the old Scholssburg, via the elevator entombed in stone near the Schwabentor, for a beer in the Biergarten and some frites to ease your guilt from visiting a chain from home.
Happy Fast Food Eating!