This 1888 painting shows the auditorium of the Burgtheater in Vienna; hence the title, Zuschauerraum im alten Burgtheater in Wien.
The room itself still looks much the same—if you scroll most of the way down on this site on the theater, you’ll see a recent picture of it—though the seats have been slightly reconfigured and many electric lights have been added.
With its highly detailed crowd scene, its lovely composition, this painting is pleasant enough. Unremarkable, but pleasant enough.
Except it is remarkable. It’s remarkable, because it’s the work of a man you’ll know for his “sumptuous, ornate paintings in which the figures are nearly submerged in a mosaic of jewel-like color and gold” (as the Getty puts it).
It would be a decade before he really developed that style, though, the style that made him famous—and made him so entirely outside of art history.
This is the work of one Gustav Klimt.