The Moonstone Mask is a posh tavern run by Ophala Cheldarstorn in the merchant quarter of Neverwinter. In the past, the Mask was also a brothel, where people would go for "privacy." More recently however, Ophala has converted into a a ritzy nightclub, much to the chagrin of Neverwinter's middle-class residents, and began to phase out it's previous functions.
The Moonstone Mask was a location in both Neverwinter Nights games.