Stockholm rain is rarely dramatic. It's a gray, persistent, two-day affair that arrives in October and visits again in March, and pretending it isn't happening is the local sport. The good news is that the city is built for it. Most of what makes Stockholm worth dating in is indoors anyway.
Start at a museum, but pick the right one
The Vasamuseet on Djurgården is the obvious move and it's obvious for a reason: a 17th century warship, raised whole from the harbor mud, sitting in a purpose-built dark hall. It's atmospheric and it kills two hours easily. The downside is the tourist density. Go on a weekday afternoon if you can.
For a quieter date, Moderna Museet on Skeppsholmen is the right call. The permanent collection has Picasso, Dalí, Rauschenberg, and the building has long windows facing the water. The cafe upstairs is one of the best museum cafes in the city and you can stretch a coffee for a long time. Fotografiska on Stadsgården is the third option, especially if you want something more contemporary. The top-floor restaurant has the view, and the museum stays open until eleven most nights, which makes it a useful evening move when a dinner-and-walk plan has been rained out.
Spend an afternoon in a department store
This sounds joyless and it isn't. NK on Hamngatan is a hundred and twenty year old department store that functions, in bad weather, as a kind of indoor town square. Go to the basement food hall, get pastries from Vete-Katten's outpost or oysters from the seafood counter, and then wander the floors without buying anything. The same logic applies to Åhléns City at Sergels Torg if you want something less expensive.
Östermalms Saluhall, recently renovated and back in its original 1888 building, is better than either for the food angle. Two glasses of wine and a plate of shrimp at Lisa Elmqvist's bar is a complete date in itself.
Cafes that hold up for three hours
The Stockholm cafe is built for sitting. Vete-Katten on Kungsgatan has been doing it since 1928 and the warren of small rooms means you can almost always find a corner. The princess cake is the order. Cafe Pascal on Norrtullsgatan in Vasastan is the modern equivalent, brighter and more crowded, with the best cardamom buns in the city. Drop Coffee on Wollmar Yxkullsgatan in Söder is the serious-coffee answer.
For a longer sit with a drink involved, Tweed on Linnégatan does a proper afternoon-into-evening transition. You arrive for tea, you stay for whisky.
The pool option
Centralbadet on Drottninggatan is the move I keep coming back to in winter. The 1904 pool hall is beautiful, there's a sauna, and a few hours of getting warm and getting in and out of water is unexpectedly intimate without being too much. Sturebadet in Östermalm is the fancier version. Both work as a third or fourth date when you've already established that you want to keep seeing each other.
A long lunch as the whole plan
In bad weather, a long lunch is underrated. Pelikan on Blekingegatan does Swedish husmanskost in a wood-paneled beer hall room that has not changed meaningfully since 1904. Order the herring plate and a beer, take three hours over it, walk out into the dark. Tennstopet on Dalagatan in Vasastan is the same idea on the other side of town.
For something less heavy, Babette on Roslagsgatan does pizza and natural wine in a small warm room and it's almost impossible to have a bad time there.
What to do between things
The trick to a rainy Stockholm date is keeping the indoor stretches connected. The tunnelbana is your friend: every station is its own small art project and Kungsträdgården, Stadion, and T-Centralen are worth the platform time. The pedestrian tunnels under Sergels Torg and Slussen mean you can move between Norrmalm and Söder without spending much time outside.
And if all else fails, Hötorgshallen, the basement food market under Hötorget, is a good emergency stop. Buy a kebab from Kajsas Fisk or a bowl of soup, sit at a counter, and let the rain do whatever it's doing.