[divbzero]

Construction on the Basílica de la Sagrada Família began in 1882 and was less than a quarter complete when its architect passed away in 1926. [1]

[1]: https://en.wikipedia.org/wiki/Sagrada_Família

It remains a work in progress today.

[winfred]

That goes for all cathedrals though. Just two random examples, Notre Dame took about 100 years for the main structure, Cologne Cathedral took 600 years.

https://en.wikipedia.org/wiki/Notre-Dame_de_Paris

https://en.wikipedia.org/wiki/Cologne_Cathedral

[genera1]

And is usually a matter of funding, famously Hagia Sophia was built in five years

[prawn]

Crazy Horse Memorial has been dragging out too. Got the impression that what exists now is functional enough to serve as a tourist trap so there's less incentive to complete it.