Dohány Street Synagogue, largest synagogue in Europe and fifth largest in the world. I have to swing by again because I was there so early it was closed.
It was completed in 1859 in the Moorish Revival style. There were many other buildings too reminding me that Hungary was part of the Ottoman Empire from 1541 to 1699.
The structure suffered severe damage during WWII and was not restored until 1991-1998.