Fodor's Expert Review Basilique Notre Dame d'Heliopolis

Also known as Our Lady of Heliopolis Co-Cathedral, this Roman Catholic basilica was designed by Alexander Marcel, the designer of the Baron Empain Palace, who modeled it after Istanbul’s Hagia Sophia. Hidden beneath its altar is a chamber containing the remains of Baron Empain—a significant figure not only in Heliopolis’s history, but in the cathedral’s inception—and his family. The church is open to the public (call ahead to confirm hours), but you must prearrange permission from the lay council to access the crypt.