I have successfully both entered and escaped the legendary Château d’If!

The real-life Château d’If is almost exactly as described in Dumas’s The Count of Monte Cristo. A stern 16th century castle on a tiny fortified island offshore from Marseilles, with strong walls, dank cells, and few visitors.

The tourist authorities have helpfully labeled one cell as they very one where Edmond Dantès, the Comte de Monte Cristo, had been held. And it comes complete with a narrow roughly cut escape tunnel!

Fortunately, in reality the modern guards are happy to let visitors enter and leave for only 6 Euros. (The spoon hidden in my sock was quite unnecessary.) But back in the day, it really was a very secure prison, analogous to Alcatraz. Outside of fiction, no one is ever known to have escaped.