This recently reopened day spa, located in the Seagate section of Brooklyn, caters to the local Russian community—which makes perfect sense, as it was inspired by a Russian-style banya. Indeed, authenticity reigns at the convivial Mermaid Spa, where there are multiple Russian steam rooms, including a Turkish bath and two Russian baths, a dry sauna and two cold pools fed with chopped ice. And if you work up an appetite with all that relaxing, there's also an attached restaurant that serves Russian dumplings.