In 1873, the castle was purchased by a couple, who restored it; the town re-purchased the Grimaldi castle in 1937, and it was registered as an historic building in 1948. Today, the Grimaldi Castle-Museum houses various art exhibitions and welcomes visitors from all over the world. (Source: Office of Tourisme)
From Nice, you would take bus #200, 94, or 400 and get off at the main square (gare routiere), called “Square Bourdet” in Cagnes-sur-mer. Then, just a few steps away, there is a bus stop to take the free shuttle (#44), that runs every 15 minutes up to the village (Chateau stop). The streets are steep and windy, and therefore, this village is referred to as the Montmartre of the French Riviera (musical video in this link). There are also pedestrian access paths from below, if you are feeling energetic!
For the size of the village, there are quite a few restaurants. I have eaten in the main square at L’Atelier, Le Jimmy’s, and Les Baux, and (within walking distance) at Le Manoir and La Goutte d’Eau (favorite being Les Baux due to its sunny terrace, and ambiance-this restaurant will be moving to Nice in June, 2014), although all of them have good food and a friendly, village atmosphere.
This charming village is a nice day-trip getaway, without being too far away from Nice!