Sagrada Familia, Barcelona, Spain

In the late 19th century, a huge contest was held for plans of the new cathedral, and when one was finalized, the cornerstone was layed in 1892. The crossing, sanctuary, and chapels radiating around it were built in the Byzantine-Romanesque style, but the original architect was dismissed in the early 20th century. The remainder of the cathedral was to be complete in the Neo-Gothic style, this includes the nave. Over a century later, and the 3 towers (one above the crossing and two on the west front) along with the transept were never finished. Lack of interest and funding halted any construction since the '90s. There was a fire in the unfinished north transept, which damaged the gift shop and destroyed valuable tapestries. In 2008, the cathedral leased some of its land for a glass apartment tower, and more recently, another lease for 99 years. This one allowed two residential towers to be built right along the north side of the cathedral, but at least they earn $3 million per year, which could be used for completing construction! Sadly, the cathedral is not designated a NYC landmark, which might potentially put it at risk for demolition for further development.