A rainy day in Seoul does not always need a new itinerary. Light rain may only call for shorter walks and longer breaks; heavy rain can make an outdoor district impractical. Keep the replacement on the same side of the city when possible.
Shorten the route before replacing it
Keep one nearby museum, café or shopping area as a pause if the group can manage wet pavements. A central museum works when it connects to the day’s existing lunch and hotel route. Going across Seoul for an indoor stop can cost more time than the rain saves.
If the main plan is outdoors—a lake walk, market, park or hill—decide whether the group still wants to go in wet shoes. If not, replace the whole block with an activity that suits the weather, rather than stacking unrelated indoor attractions on the original route.
Make the hotel break useful
Rain and wet clothes make a midday return valuable for changing shoes, drying a coat or resting before dinner. Place that break near where the group already is. For a late arrival or airport connection, do not move luggage across town just to reach an indoor attraction; start with the Seoul base guide and the route to the next stop.
Before setting out, confirm that the museum or ticketed activity is open on that date, whether timed entry is needed and how long the indoor queue may be. Keep one nearby alternative so a full session does not depend on a single reservation.
If the rain is light and the group still wants the original neighbourhood, shorten the outdoor section and add a dry stop. If the weather makes the walk itself uncomfortable, move the whole day’s focus indoors and keep the return simple.