Stockholm has roughly five months a year of weather you'd voluntarily go outside in. The other seven months are why the city has such good cafes, baths, and museums. Here's how to spend a long rainy afternoon on a date without ever really going outside.
The bath as a whole afternoon: Centralbadet
Centralbadet on Drottninggatan is a 1904 Jugendstil bathhouse with a pool, sauna, steam room, and a restaurant, and a day pass runs around 350 kronor. As a date it has a strange and useful pacing: you swim, you sauna, you sit, you swim again, three hours go by. The pool hall itself, with the painted ceiling and the colonnade, is one of the most beautiful rooms in central Stockholm and most visitors don't know about it.
The upgrade is Sturebadet in Östermalm, which is fancier and more expensive. The downgrade is Liljeholmsbadet in Liljeholmen, the floating bathhouse from 1929, which is cheaper and weirder. All three work as dates.
A long museum afternoon, planned right
The right rainy-day museum in Stockholm is Moderna Museet on Skeppsholmen. The collection is good, the building has long water-facing windows, and the cafe upstairs serves a proper lunch. Two hours in the galleries, one hour in the cafe, you've used up half an afternoon and barely noticed.
Fotografiska on Stadsgården is the alternative for a different mood. The exhibitions rotate every few months, the building is an old customs house with industrial bones, and the top floor restaurant has the best museum view in the city. Open until eleven most nights, which makes it the right call if dinner-and-a-walk has been rained out and you need to slide a date into evening territory.
If you want to learn something together, Tekniska Museet out at Museiparken does interactive exhibits that are surprisingly fun on a date. The science-museum-as-date sounds dorky and it works.
Bookshops you can actually spend an hour in
The Stockholm bookshop date is underused. Hedengrens at Sturegallerian has the best English-language section in the city and the upstairs is quiet enough to actually browse. Söderbokhandeln at Götgatan 35 is the Söder equivalent, smaller and more political. Papercut on Krukmakargatan does art books, magazines, and small-press fiction in a way that takes commitment to browse properly.
The move is to give yourself a low-stakes assignment: each pick a book for the other person, ten kronor budget cap if you want to make it a game. Then walk to a cafe and read the first page out loud.
A cafe that holds up for three hours
The Stockholm cafe is engineered for sitting. Vete-Katten on Kungsgatan has been the gold standard since 1928 and the layout, six or seven small connecting rooms, means you can almost always find a corner. The princess cake and the semla in season are both right.
Cafe Pascal on Norrtullsgatan in Vasastan is the modern equivalent, brighter and more crowded, with what I think are the best cardamom buns in the city. Drop Coffee on Wollmar Yxkullsgatan does serious coffee in a small warm room.
For a longer sit that includes alcohol, Tweed on Linnégatan transitions cleanly from afternoon tea to evening whisky and the leather chairs are made for it.
The food hall as a date
Östermalms Saluhall, the 1888 food market on Östermalmstorg, is back in its original building after a long renovation and it's one of the best rainy-day dates in the city. Two glasses of wine and a plate of shrimp at Lisa Elmqvist's bar runs around 400 kronor for two and takes an hour. After that you wander the stalls, buy cheese and bread you don't need, and end up at the cafe at the back for coffee.
Hötorgshallen in the basement under Hötorget is the cheaper, scrappier version. Less of a date room, but the food is good and you can move on to a film at Filmstaden Sergel or a coffee at Vete-Katten without going outside.
A practical chain
The rainy-Stockholm date works best as a chain of indoor stops with short transit between them. A three-stop afternoon I'd vouch for: start at Moderna Museet on Skeppsholmen, take the 65 bus to Östermalmstorg for a drink at Saluhall, walk five minutes to Tweed on Linnégatan for whisky as it gets dark.
Three rooms, four hours, almost no time outside. That's the whole game.