Old Jewish Quarter
The Josephov district is bounded on the west and north by the curve of the Vltava River and is just a hop-skip-and jump from the Old Town Square but for hundreds of years it was considered a separate town. It was a Jewish ghetto for nearly 700 years, from around 1180 or so until about 1850 — the later date being a good 70 years after the incorporation of Josephov into greater Prague. Around the same time it underwent a major transformation with swampy areas (it is near the Vltava River and subject to flooding) filled and many ancient, narrow alleys replaced by a more modern grid of fewer and wider streets.
Until the Nazi deportation of Jews to nearby Theresienstadt, where they ran a concentration camp intended to fool the world into thinking Jews were receiving humame treatment, Josephov had a lively and dense Jewish life. Today five synagogues and a cemetery remain of that life. All but one of them is a museum. Together they are the antithesis of what Hitler intended: that a museum be created as the sole reminder of a long disappeared people. Instead they provide a poignant reminder of the strong culture that once resided in this district — and the continuity of Jewish life.
Terezin is the modern, Czech name for Theresienstadt. It is about 30 miles (50 km) to the north of Prague and a frequent day trip for those who have the time. During WWII more than 90% of the Jewish population of then Czechoslovakia died in Nazi run death camps. Those in Theresienstadt for the most part slowly starved. Toward the end of the war the survivors were transfered to other camps where they were immediately put to death.
The Old-New Synagogue (I've forgotten the reason for the name, but I think it was because later there was a new new synagogue) holds services on Friday night. When we were in Prague I attended them; the congregation of about 100 people seemed to be made up of half local people and half Americans visiting. Getting in required going through a security check.
You can get a good idea of the area by walking around and seeing the Synagogues from the outside. Be sure to look for the clock with Hebrew letters/numbers. If you buy a ticket to the synagogue-museums you will get a good introduction to Jewish history. Each building specializes in a different aspect, e.g. Jewish holidays. Save this for your second or third day, if either you have seen what you want of the streets of Prague or it is too cold to be outside.
The Old Jewish Cemetery contains about 12,000 tombstones, but estimates of the number of people buried there are much higher. Many graves are stacked on top of one another, and a single tombstone may stand over as many as 12 graves. Adjacent to the cemetery is the building of the committee that ran the cemeteries. The committee formed one of the most prestigious groups in the Jewish community.