Empire of the Dead! I loved the catacombs. Stacks and stacks of bones and skulls. Thankfully I journaled about visiting and have a great description about descending on a spiral staircase and walking a ways before seeing the stacks and then another spiral staircase back up, which was disorienting. Luckily Paris has so many metro stations that we just found one and made our way to Versailles. I can't believe the sheer number of bones there were and it was mostly the long bones and skulls which isn't surprising they preserve the best. Some of the caverns were massive reaching 50 or more feet back and stacked 10 feet high.
Only one photo turned out due to the extreme darkness. I was going for a creepy vibe but didn't quite hit that note for me.