The Villa Wesendonck, now part of the Museum Rietberg complex in Zurich.
One of several Richard Wagner sites in Switzerland, though the Rietberg is devoted to Asian/exotic art and has nothing to do with Wagner.
The villa was the home of conductor Otto von Wesendonck and his wife, Mathilde.
Mathilde provided the inspiration for Wagner's Tristan und Isolde, and he set her poetry to music in the famous orchestral song cycle, the Wesendonck Lieder which include several references to the Tristan score.
In "The Master Musicians: Wagner" Barry Millington writes:
"Their relationship was intimate, but as was suggested earlier, probably stopped short of the sexual act. Consummation would have shattered the dream and made it impossible to write Tristan und Isolde, the ultimate glorification of love."
Wagner himself wrote:
"As I have never in my life tasted the true joy of love, I will raise a monument to this lovliest of all dreams....."
As I recall, the villa can be seen in one sequence in the 1955 Wagner film biography, MAGIC FIRE.
For another even more bizarre take on Wagner see Ken Russell's LISZTOMANIA.