The elegant little Gaiety, opened in 1871, hosts a varied array of performances, everything from opera to classical Irish plays and Broadway-style musicals. (The Gaiety’s annual pantomime, or Christmas show, is a big event in the city’s theatrical calendar.) And when the thespians leave, the partygoers arrive: On Friday and Saturday from midnight on, the place turns into a nightclub, with four bars hosting live bands and DJs, spinning R&B, indie, blues, or hip hop. There are even occasional cult movie showings. Don’t forget to check out the ornate decor before you get too tipsy.