Make a rainy-day alternative for your Korea itinerary
Pair an outdoor plan with an indoor option in the same area, and check the route between them. A roofed attraction is only useful if you can reach it and enter it on the day.
Keep the alternative nearby
Choose a museum, exhibition or other indoor visit that fits the same part of the city as your original plan. Check its opening day and reservation requirements in advance. Avoid replacing a short outdoor stop with a long cross-city journey simply because the alternative is indoors.
Check the forecast for the right place
Use Korea Meteorological Administration information for the destination, not only the city where you slept. Review current forecasts and notices before heading out. A broad seasonal description is less useful than the conditions for your actual route and time.
Recheck activities exposed to weather
For observatories, coastal activities or other outdoor facilities, look for an operator notice as well as the forecast. An attraction's usual hours do not establish that it will operate during adverse conditions. Follow closures and local instructions rather than trying to preserve a fixed itinerary.
Use a clear decision point
Decide when you will switch plans, such as before leaving the accommodation or before a reservation's cancellation deadline. Tell your group where to meet under the revised plan. Keep the indoor venue's address and ticket details with the original itinerary.