The church of Santa Engrácia in Lisbon, which took about 300 years to complete, is now the National Pantheon. It was designed as a massive Baroque centralized plan, and what we see above was actually finished almost 300 years later in 1966. In the meantime, the ultra-morose building process (even for Portugal!) gave birth to a popular expression: obras de Santa Engrácia, or works of Santa Engrácia, used to refer to anything which takes forever to be completed. But completed it was, and the dome stands beautifully stark in its red and cream scalloped composition.
Lisboa, Panteão Nacional.