Konstanz is a city at the Lake Constance in South Germany at the Swiss border.
To get to any city in Switzerland go to the main border and hold up your sign at the parking lot on the Swiss side. Just a couple of meters behind it the highway A7 starts.
If you want to go to Ravensburg it is best to take the ferry to Meersburg. It usually goes 4 times an hour, at night just once every hour. Ask the people who drive there eighter while waiting for the ferry or in the little café on the ship. If it is cold or raining you can wait in a heated waiting room until the ferry arrives.