In 2018, I visited Fort de Regret in the Verdun area.
This fort, and others nearby, were built between 1875 and 1877 to deter German aggression and were modernized between 1905 and 1907 with additional concrete and weaponry.

During World War I, in 1915, the weapons and munitions were dismantled, and the garrison was withdrawn.
When Germany attacked the Verdun sector in 1916, the fort was hastily reoccupied and used as an artillery observation post.

Between the World Wars, the fort was not maintained and remained unoccupied.

During World War II, in June 1940, German troops occupied the fort without a fight/after a short fight (sources differ). I assume these photos were taken on the day the fort fell.
After World War II, it was left as it stands today.

I recently found these old photos online and was surprised by how many angles matched my own photos. Today, the fort remains in good condition, with most of the interior accessible, although getting there requires some hiking and climbing.

Photo taken from the Salthouse dock

https://youtu.be/vqACS__2WSo?si=WKBeJ_34pOyBwl_v