In Prison de Joaquin's Altar of Despair (F6), lies the Tombstone of Vernal, with the following engraved message:
When war raged across the country, the Prison de Joaquin, whose Iron Door had been locked for Three-Years, was completely forgotten. Within that enclosed space, the dying prisoners turned into monsters. They killed and ate each other. The place was rapidly becoming a living hell. "Why did they shut us in here?" "Why hasn't our suffering been reported to the outside world?" The prisoners devoured each other and became increasingly insane. The vindictive spirits mutated into monsters and now they cannot live as human beings. To whom it may concern, I wish you pray for our spirits by lighting up the 24 candles that are built deep inside the prison.
In the next floor of the prison, the Torture Chamber, there are 24 Torches of Bernal (Lv.75) located in the middle of the map, near F3. The torches have 3 possible states - unlit, lit, and smoking. Lit and smoking torches cannot be attacked. If an unlit torch is attacked, it becomes lit.
Once a torch is lit, it remains so for about 5 minutes, after which it becomes smoking. A smoking torch refreshes to its unlit state after 12 or 24 hours (uncertain; confirmation needed).
If all 24 torches are lit within 5 minutes, Soul Mothtein (Lv.100) spawns in the area. Soul Mothtein uses elemental strife and hole of darkness repeatedly. Catherine is somewhat useless here (except for lighting the torches), since her dolls keep dying in the AOEs. You may want to use apocalypse or similar skill to lock his skills. He is solo-able; I managed it in Carracci server with +5 Lv.84 elite armors and Lv.92 elite weapons.
This boss has been known to drop Lv.92 armor, rings (e.g. elemental strife), and Lv.84 elite equipment (rare). Also, see IAHGames forum topics - Prison Torches and Tombstone of Vernal.
P/S: Is it Vernal or Bernal? Once again, a name is lost in translation. They can't even standardize the names properly...