Where is the second face in a graph with 3 nodes? I understand that to work out the number of faces of a connected planar graph, you use Euler's formula F = A - N + 2, where A is the number of arcs and N is the number of nodes.

For a triangle node (3 arcs and 3 nodes), the number of faces would therefore be 3 - 3 + 2 = 2.

But I can't count two faces, only one (the triangle itself). Where is the second face, or where have I misunderstood?
You probably smack your head against the wall for this but: One face "inside" the triangle, the other one is "outside".