The images depict a 1+1 dimensional slice of the Schwarzschild-deSitter black hole spacetime, isometrically embedded into 2+1 dimensional Minkowski space, which is identified with Euclidean 3-space. Cross your eyes to see a stereogram. The four regions of the Penrose diagram of the slice are each a different color; the prominent ``X'' containing the origin (where the four regions meet) is the horizon of the hole. In order to view the pair properly, your browser window must be wide enough to show both frames, but not so wide that it is difficult to cross your eyes far enough to merge the images.
For mathematical details, please see Spacetime Embedding Diagrams
for Spherically Symmetric Black Holes, by John T. Giblin, Donald
Marolf, and Robert Garvey:
The figures below were created with ePiX from John Giblin's Maple code, cf. Figure 7 of their preprint.