Aarhus weather is honest. It will rain, it will be grey, and pretending otherwise ruins more dates than the rain itself does. The locals who date well here build the weather into the plan instead of fighting it.
Spend three hours at ARoS without rushing
ARoS is the obvious answer and it earns it. The rainbow walkway on the roof is the photograph everyone takes, but the date happens downstairs in the permanent collection and the basement installations. The Boa room and the James Turrell pieces in the lower levels are designed for slow looking, which is what you want when you're getting to know someone.
Buy a year pass if you live here. It pays for itself in two visits and turns the museum into a default move whenever the forecast turns. The cafe on the ground floor is fine for a coffee break in the middle. Plan two and a half hours minimum.
Den Gamle By in heavy weather
Counterintuitive, but Den Gamle By is better in the rain than in sunshine. The crowds thin out, the cobbled streets get atmospheric, and the indoor exhibits in the 1974 quarter and the 1927 apartment building become the main event instead of a sideshow. The bakery in the old town serves proper kanelsnegle and the coffee shop in the 1974 section is a strange, lovely time capsule.
Go on a Tuesday or Wednesday afternoon if you can. You'll have most of the buildings to yourselves.
Bruuns Galleri and the cinema
The Bruuns Galleri cinema is underrated for dates because it's attached to enough other things that you can build a whole afternoon around it. Coffee at Original Coffee on the ground floor, a film, then dinner at one of the M.P. Bruuns Gade restaurants when you come out. The walk between is all indoors or covered.
If you want something more arthouse, Øst for Paradis on Paradisgade is the proper Aarhus cinema. The lobby bar is a date in itself. Get there forty minutes before the film and you'll see what I mean.
Coffee crawls in the Latin Quarter
When it's raining steadily, do a coffee crawl through the Latin Quarter. La Cabra on Graven for the first one, Great Coffee on Klostergade for the second, and Stillers Boghandel around the corner if you want to break it up with a bookshop. The streets are short enough that you only get rained on for thirty seconds between each stop.
This works because it gives you natural transitions. Each new cafe is a small reset, a new seat, a new excuse to keep talking. Three hours pass without anyone noticing.
Dokk1 as a meeting point
Dokk1 is technically a library but functions as the city's living room. On a rainy Saturday afternoon, meet there, find a corner with a view of the harbor, and bring something to do. Chess sets are available at the front desk. The cafe on the ground floor is unremarkable but cheap.
This is a low-stakes second-date move. Public, free, easy to extend if it's going well, easy to end if it isn't.
Salling rooftop, even in the rain
The Salling rooftop has covered sections and a heated bar, and being up there in actual weather is more interesting than being up there on a sunny day. You can see the rain moving across the city and the harbor going grey. Order a glass of wine and stay forty-five minutes.
It sounds like a tourist move. It isn't, if you go on a weekday after work. Locals use it as a quick drink before dinner more than visitors realize.
The pragmatic rule
Build every rainy-day date around two indoor venues within four minutes of each other on foot. That's it. The rain becomes a feature instead of a problem because you're always almost arriving somewhere. Aarhus is small enough that this is always possible. Use it.