The Cafe Carnegie is a separate entity from the museum. It is laid out nicely but can be very costly when you are having lunch. They also have a coffee and full bar on site as well. It is usually best to make a reservation since the place gets fairly crowded over the lunch hour. I had one and was deciding whether I wanted to go with a salad or panini. They are now full table service. They serve brunch on the weekends.
I opted for the latter and had the grilled zucchini panini with avocado, mozzarella, and other things on their homemade sourdough bread. I had read that all their sandwiches are made with homemade bread. The sandwiches with the exception of one all come with an order of French Fries.
I got my order and noticed it was slightly burnt along the edges but it didn't stop me from eating it. It actually didn't seem to have much of a flavor nevertheless I found it very filling. I really on the other hand enjoyed the French fries that went with it. The waitress staff were both friendly and helpful.
This is an okay business for one or two people having lunch but if you are bringing a family it can get pretty costly and there are very few items on it for kids. I believe the museums have another cafe in the basement which is supposed to be more family friendly but I have not had an opportunity to check it out.