Every year in October there is the
Architecture Week in Madrid. It's like the
Open House Weekend in London or Chicago, or the
Doors Open Days elsewhere. So some buildings that are not usually open to the public for free, can be visited then. For instance, last time I went, with my camera and a wide-angle lens, to the Circle of Fine Arts. It's an eclectic-style building from the 1920's. This is the staircase:
The ballroom:
I placed myself under the dome and took a photo of it. Obviously, I had to use a wide-angle lens (10mm-18mm, in this case):