Just adding a review to note that, until December 31, 2024, there is an exhibit at the Hôtel Van Eetvelde (one of the Horta townhouses) entitled "Stoclet 1911 - Restitution". The exhibit includes a "virtual reconstruction" of the Stoclet House interior -- basically a CGI video, but one that gives you a fairly good sense of what the inside of the structure looks like, or what it looked like in 1911. (Think acres of clashing marble, covering every square inch.) The exhibit is the result of a collaboration of the Architecture Faculty La Cambre Horta and the Art & History Museum of Brussels, where it was displayed last year. it's not a perfect substitute for a visit, but it did suffice to provide a somewhat specific impression of the building's interior, and -- coupled with a glimpse of the building from the sidewalk -- was enough for me to consider the site "visited".