We
are at the entrance to the underground passage leading to the
northern casemates.
They were built in 1827, under Charles X, to house a "reverse
firing battery" intended to protect the rear of the Fort.
In
1994, restoration work began on these casemates, which had largely
collapsed. They are now open to the public.
Today,
after having been an exhibition and restoration room, it houses
the Escape Game "Fort escape Seyne" which can be booked
on the website: https://www.fort-escape-seyne.com