Icon under a microscope

tHis landmark is iconic and easily recognisable when you see the whole picture, but can you identify it from this small portion of the image?

This church is breathtakingly beautiful, despite the fact that it remains unfinished.

In fact it began its construction way back in 1882, and only in 2010 did it pass the midway point of the build.

It is a mix of gothic and art nouveau architectural styles.