An icon of the city, the Dom was built in the 15th century as a Roman Catholic church. The church was Lutheran since 1539, Calvinist since 1613 and from 1817 Evangelical Protestant as it is today.
A visit of the Dom is recommended if you find yourself on the Museum Island, on the Mitte district of Berlin.
You can find a lot about the history of the place and the reconstruction after the damage of the allied bombing in WWII. The Berliner Dom reconstruction started in 1975 and was completed in 1993.
Be prepared to climb some steps in order to reach the dome and spend some time there enjoying a very nice view of central Berlin.
The church crypt is also quite impressing; it contains 94 entombments of Prussian kings and queens. The Hohenzollern Crypt is one of the most important royal burial places in Europe and you can see that just by looking at the impressive coffins.
The Berliner Dom in Mitte, Berlin
View of Museum Island from the Cathedral dome, Berlin 
Berliner Dom seen from the Alexanderplatz TV Tower 
Berliner Dom crypt 
