The mistake people make on a rainy date in New York is treating each indoor stop as a quick shelter between transit. The better move is to pick one or two places that are good for staying. These are rooms that hold up for hours.
Grand Central, slowly
Grand Central Terminal is a building New Yorkers walk through on autopilot and rarely actually look at. On a rainy day, treat it as a destination. Start in the main concourse, look at the ceiling, then walk down to the lower-level food court. The Oyster Bar has been there since 1913 and the saloon room in the back is the move. Half a dozen oysters at the counter is around 20 dollars at happy hour, which runs weekdays from 4:30 to 7. The whispering gallery outside the Oyster Bar is a real acoustic trick and worth two minutes.
Upstairs, the Campbell on the southwest balcony is the bar built into the old private office of a 1920s financier. Cocktails are 22 dollars and the room is the room. One drink there, then the train home. You have spent 90 minutes and seen three different parts of one building.
A long cafe, the kind that lets you stay
Not every cafe in New York is built for staying. The ones that are: Cafe Reggio on MacDougal, which has been there since 1927 and never rushes anyone. Cafe Sabarsky in the Neue Galerie at 86th and Fifth, where the coffee is Viennese and the Klimts are upstairs. Cafe Lalo on West 83rd, less busy now than when it was in the Tom Hanks movie, which is part of the appeal.
In Brooklyn: Cafe Regular du Nord on 11th Street in Park Slope is small enough that you have to sit close. Konditori on Bedford in Williamsburg is good for a two-hour sit because the chairs are actually comfortable. Variety Coffee on Graham has more space than most.
Order slowly. Get a second drink. The cafe date works if you let it.
The Morgan Library, which most people forget about
The Morgan Library at 36th and Madison is what people are imagining when they think they want to go to a museum on a date. It is the converted private library of J.P. Morgan. The original library room with the three tiers of books is one of the more impressive interiors in Manhattan and the rotating exhibits are usually small enough to actually finish. Admission is 25 dollars and free on Fridays from 5 to 7pm.
The attached cafe in the glass atrium is open during museum hours and a cup of tea there is the right kind of indulgence. Plan two hours.
An indoor market, used as a date
Chelsea Market on Ninth Avenue between 15th and 16th is too crowded on weekends. Go on a weekday afternoon when it rains and it is fine. Los Tacos No. 1 is the anchor. Miznon, Very Fresh Noodles, and Creamline are the next tier. Walk slowly, share three things, end at the bookstore Posman Books inside the market.
In Brooklyn, Industry City in Sunset Park is the same idea with more space. Avocaderia, Japan Village, and Sahadi's all have counters. The whole complex is indoors and connected, which means you can walk for an hour without going outside.
A bookstore that is also a destination
The Strand on Broadway and 12th is the obvious answer and still the right one. Three floors, including a rare books room, and dense enough that an hour passes quickly. McNally Jackson on Prince Street in Nolita is the upgrade for people who actually read fiction. Books Are Magic in Cobble Hill, on Smith Street, is small but feels like a real place because Emma Straub still runs it.
The game in any of these is to pick a book for the other person within twenty minutes. Under twenty dollars. Explain why. It is a better conversation than most you will have at a bar.
A specific museum that is not the Met
The Tenement Museum on Orchard Street runs guided tours of restored apartments at 103 and 97 Orchard. Tickets are around 30 dollars and tours run 60 to 90 minutes. You learn something. The Frick is back at its original mansion at 70th and Fifth after the renovation and is one of the best small museums in any American city. The Cloisters up at Fort Tryon Park is a longer trip but the medieval garden room is the kind of place that justifies a wet afternoon on the A train.
A jazz matinee
Smalls on West 10th runs an afternoon set on weekends starting around 4pm, cheaper than the night sets and less crowded. Mezzrow does a similar thing across the street. A rainy Saturday afternoon, two drinks, a single set, and dinner after at Joseph Leonard on Waverly or Via Carota on Grove. That is a full date built entirely indoors.
The point
A good rainy-day date in New York picks one room that you would happily stay in for two hours, and one room you walk to after. Two rooms, one transit. Anything more elaborate is how you end up wet and irritated on a corner trying to find a third place. The city has more good rooms than almost anywhere. Use one.