It was somewhat providential that the first time we were in Keyserberg, it was due to a two hour car related delay (from a loose pickup wire on the distributor of my 1987 Saab Cabrio). We had modified our day's travel plans, and decided to not travel too far. We drove on to Keyserberg (10 km), where we climbed to the ruined castle, and stopped for beers in the main square (necessary for our nerves, of course).
The Chateaux is open year round, and is a short walk from the main square of town (about 300 meters, uphill). There is no charge to visit the castle. There are no public bathrooms at the Chateaux.
We’ve had the opportunity to go back to Keyserberg as late as 2007, and the town was as lovely as we remembered.