Impressive chateau, several hundred years old, with a moat still in place and walking bridges to enter. Ramparts can be toured for free and offer excellent views when the weather is nice. The museum(s) are two parts with one currently housing an exposition on the Mongolian Empire Genghis Khan - mostly in French, but you can download the exhibit app (QR codes available on site) to help guide you through. The museum of Nantes inside the largest part of the chateau is truly great. Be sure to get an audio guide (2 Euros each) and take your time. The entire audio guide tour itself lasts 3 hours, but you can pick and choose what makes the most sense for what you want to see. Ticket includes entrance for exposition and the Nantes museum (separate buildings), so don't throw your ticket away. Lifts are available for both as there are many floors accessed via very old winding steps - the Nantes museum is in the tallest of the buildings, so be prepared to walk and climb stairs. The exhibits though were well worth it. Everything from seeing foundations from Roman-Gallo times 2,000 years ago to explanations of the history of the city and its rich maritime history. The room with paintings and background on the French Revolution was especially notable given what true terrors took place here. Also be sure to focus on the Edict of Nantes portion which is towards the very beginning of the tour. You could easily take two days here, or at least one very long day to see it properly. Gift shop at the end of the Nantes Museum has lots of books and some souvenirs as well.