Start with one exhibition
Choose an indoor visit you actually want to make. Museum Kampa is one nearby option for modern art. Check the exhibition programme, ticket conditions and opening times, then build the rest of the day around that one confirmed stop.
Shorten the outdoor stretches
Use a live public-transport planner instead of committing to a long wet walk. Give yourself time to dry off before the next activity. Cobbled streets and steps deserve extra care in the rain.
Leave the evening open
A good travel day does not have to be full. Return to your room, change the plan and choose another outing if the weather improves. For groups, agree on an indoor meeting point before splitting up.