Argentinian Artist Leandro Erlich creates solid works of marvelous illusion. Swimming pools viewed from beneath become the viewing experience of those viewing from above. A ladder reaching up to a window that floats in the sky. A hotel hallway seen from above displays museum visitors floating in air.
Here is one image from his 2004 installation piece Bâtiment.
Nuit Blanche. La Cour de l'Observatoire de Paris
More info on Erlich can be found here and here.