In Curse Of Strahd, the Pack followed a Tarokka Deck prophecy to recover the Tome of Strahd at the bottom of the Pool, and used it as a weapon to fight back against Strahd.
At the northern edge of Krezk were the holy waters of Saint Markovia's Pool, fed by underground rivers from the Balinok Mountains. The pool's waves sparkled even when there was no light to reflect off of them, and the waters themselves were Consecrated. Originally known as the Pool of Zachodgrad and considered the lifeblood of the otherwise-isolated fort, the Pool was given the name of Saint Alizandra Markovia after she performed a miracle there.
Prior to Zachodgrad's fall and renaming to Krezk, the fort was attacked by a Werewolf army lead by Jaghr of the Longtooth. The werewolves attacked Zachodgrad relentlessly as Barovia's woods became increasingly dangerous, and eventually, they breached the fort and attacked the townsfolk. In an epic battle, Alizandra defeated their leader at the pool. With her final smite, it was said that the sun did not set for an entire week, even as the rest of Barovia remained dark and covered in mist. The waters of the pool became consecrated with the Morninglord's divinity, and Alizandra was given the title of "Saint".
After the battle, she cured the willing werewolves of their Lycanthropy, including their subchief Ladislau Krezkov at the foot of the pool. For this deed, a statue was erected commemorating the moment, and Alizandra was given the title of "Saint". However, after Zachodgrad fell to Strahd's forces and was given to the Krezkov family, the new Burgomaster ordered an altering of the statue. Saint Markovia was removed, so only a bust of a weeping Ladislau remained, protected by a gazebo and made into a shrine.
At some point later, in a fit of madness and unbeknownst to anyone, Strahd cast his Tome of Strahd into the bottom of the consecrated pool, to ensure that he could never gaze upon its pages again.