This is a great excursion. It is best to go in the spring or fall since it is a favorite with tourists during the summer. And it is hot here in the summer.
Park your car in the lot at the bottom of the town and slowly walk up the narrow street to the top. There are lots of interesting boutiques and I was surprised to note that they offer reasonable prices. There are also restaurants along the way. i haven't eaten in any of them. But the stroll up the hill is interesting.
The ruins at the top are definitely worth the visit. There is a fee and don't forget your camera as the views from the top are wonderful. You will continue to wind your way upward to the castle ruins. If you have small children with you, don't bring them to the top. I think it is too dangerous.
Before you leave Les Baux - drive to the botton of the Village to the old stone quarry where you will find the Cathédrale d'Images. There is another fee but this is one of my favorite places. Inside the quarry is a sound and light show that changes every year. It is simply magical. I have been every year for the past 3 or so years. The past themes were Venice, Cezanne and Picasso. This year the theme is Australia.
Don't miss Les Baux!!