Judging from the wall carvings, the builders of this gloomy place must have venerated Charon — the godlike arc

Judging from the wall carvings, the builders of this gloomy place must have venerated Charon — the godlike archdaemon of death. Similar incense burners were used in his servants' rituals. The smoke coming from the eye socket was meant to symbolize a soul flying to him... Were the Sisters conducting some ritual? Maybe even trying to summon Charon himself? Terrible!