This landmark house of worship, built in 1887, was a center of Jewish life before it fell into squalor in the 1920s. Left to rot, the synagogue was restored following a 20-year-long, $20-million restoration that was completed in 2007, and it now shines with its original splendor. Museum admission includes a guided synagogue tour, which depart hourly; the last one leaves at 4pm.
In addition to the restored portion of the synagogue, there's a hall of exhibits about Jewish life on the Lower East Side, as well as special events and seminars. Note that the museum is closed on all major Jewish and national holidays.