The ornamental design for a three-dimensional poster depicting a cityscape, as shown and described.
FIG. 1 is a front elevational view of a three-dimensional poster depicting a cityscape showing my new design, wherein, frontally, the embossed shapes of a bridge and a skyscraper group are shown and, at the back, the debossed shape of a skyscraper a skyscraper pair having greater height than the frontally positioned skyscraper group is shown;
FIG. 2 is a top plan view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof; and,
FIG. 5 is a front perspective view thereof.
The rear and bottom plan views are not shown, and therefore not claimed.