The "Chantier Naval Opera" in Antibes. Chantier Naval means shipyard, Opera means opera. I'm unsure of the current purpose of this building, but the signs warn that a hard hat is required whatever you're going to do in there...

Update: according to this page; "Chantier Naval Opera" is an ancient military blockhouse; this building defended the entry to the port on the other side of Fort Carré. The disused Chantier naval was restored to become a cultural centre for exhibitions, shows and musical events such as "Music at the heart" and the "International Young Soloist Festival".