The image reflects a secret moment revealed without being disturbed. A rendevouz perhaps? It reminds me of the great work of Brassai and his photos of Paris after dark in the 1930's. Great composition.
BZ --- my kind of shot. You tell us these are lovers, but the shadows are ambiguous, as they always are in your images. It's a photograph that pulls the viewer in and draws them down through the middle of it, pulling us along those slippery stair towards the light. We want to walk quickly, though -- so those threatening "lovers" don't stop us and demand bus fare. (Vaporetto fare?)