Most of the Jewish Quarter was destroyed in the early 20th century to make it posh and Parisian, and in addition a bit more resilient to floods and fires. This is partly why you see the weirdly different ground levels between the synagogues and the other buildings, as the ground was actually raised when they rebuilt the area.
When they tore up the Jewish Quarter, they did so because it was derelict, overcrowded, and a huge firehazard. And before that time, Jews didn't have the freedom to live where they wanted. After the Edict of Tolerance by the Holy Roman Emperor, Joseph II, though, this changed and Jews were free to live outside the ghetto. That meant now the quarter could be restored and renovated.
random street in Josefov, the Jewish Quarter
They left the synagogues which are all still standing, active, and open for tourism. You can't get the feeling of the old, crowded, and poor ghetto that once was, but rather you can buy some super-expensive clothes, as all the top designers, including, ironically, Hugo Boss, have a storefront in this area now. Another weird fact is that the synagogues managed to survive WWII as Hitler had thought the district so nice, that he was going to use it as a huge "Jewish museum", to highlight his version of the history of the soon-to-be-eradicated people.
Here's a list of all the old buildings that still exist though and that you can take a look at. Also click here to see them all pinned on Google Maps.
The Jewish Town Hall
This was the main meeting point for the Jewish community and was built in 1586 by the mayor Mordechai Maisel, whose project