When out and about, look for different kinds of bridges. Keep a sharp eye out: there may be some you travel over every day without knowing it.
Talk with your child about the different kinds of bridges that you travel over. Notice what they are made out of, how they are shaped, how long they are, and how they stay up.
When back at home, invite your child to build a bridge for toy cars to travel on using toy blocks or recycled materials. Suggest possible props, like chairs, that she can incorporate in her play. Play with the cars, driving them up and over the bridge.
For an extension activity, challenge your child to build a bridge between two specific points; over a full sink, or another obstacle, is especially interesting.