We booked a tour of the catacombs with Leo and although there was a huge waiting line we skipped it to enter immediately. She knew a lot about the history and even pointed out at some injuries and diseases which had affeceted the bones. Our group could enter behind the locked doors whereas other visitors weren't allowed to follow us! She provided a lot of informations during the tour but also after as she helped us to organize the rest of our trip by sharing good addresses and sent us links about the catacombs. We saw another guide with a huge group and we were really happy to book a small group tour because the tunnels are narrow. I strongly recommend this tour.