Basement perhaps. Attic might freeze. Winter, especially in the north, can be long and dry enough that the plant may need to be dunked in water a couple of times (say, every 4 or 6 weeks, for a few hours each time) over the winter. The key is not to let it STAY wet. Soak it, then hang it back up and let it get dry again -- this prevents rotting. Some people simply put geraniums in a paper back or roll them up in newspaper. But you still would need to rehydrate every so often.