Art Nouveau Staircase by Victor Horta -Hotel Tassel, Brussels. Typically of this period the interior has elongated, curved and flowing lines. These lines are seen in the tiles, the staircase and also on the walls.
L'escalier rond - Abbaye des Prémontrés - Pont-à-Mousson - France
(would be costly architecture, but there are some elements here I like) "Stairway to heaven: The neoclassic Romanian Atheneum, constructed in 1888 by French architect Albert Galleron, is home to the George Enescu Philharmonic Orchestra.