Mikael Uhlin:
I'm pretty sure there's some real church somewhere in Belgium with a tower like that.
We are thinking alike here - and probably both spending too much time on it! My thought, allowing for this not being a widespread local look for spires in the region, is that it is possibly this one, on
La Chapelle Saint-Martin, which is similar.
The photo is quite low contrast, but
this sketch on the cover of a book about the chapel shows the beveled edges going up to the point which are clearly a feature of the one in the magazine.
It’s in the wrong place for my identification of the location, and it doesn’t have the paired openings in the belfry, but it is a landmark building, and it’s
just south of Braine-l’Alleud in Lillois-Witterzée.
Update: Although the chamfer on the steeple of
Sacré-Cœur à Braine-l'Alleud (also known locally as l’Ermite (the Hermitage)) isn’t as pronounced, it shares the general shape of the one on St. Martin’s, and has the double belfry openings as seen in the magazine, and the similar church tower spied in the region of the station at the start of
Seven Crystal Balls. Perhaps it
is a form traditional to the area, and would be found in other churches there too.
I also found
this great site, showing a rather lovely country walk starting at Sacré-Cœur, and which conveniently follows a route around the region in which Marlinspike Hall and the village seem to be set, and which shows that (in essence at least) it is still possible to walk through countryside such as Hergé drew, without having to resort to traversing the sewage works and industrial estates of Wallonia.