Mystical_Snowflake
I'm gonna be honest guys, I just finished reading up to this point, which only took three days, but the answer is obvious. If you guys think about it where was Christina's favorite place to go to, to relax and unwind, away from everything when she was still at Hogwarts. It's simple, it's the black lake. Also, in case you guys didn't know but the place where Hogwarts was built, is the very same place where Camelot stood. and the black lake, is the lake that resided near the castle of Camelot. There's a story in history that says that the lake of Camelot, was a magical place, of untold and unfathomable secrets and mysteries. It is said that this lake was so powerful that it was said that it could power on what seems an infinite level, with a magical lock, but hide it completely without anyone ever noticing it. That means, all you need are the keys to unlock the lock. Pretty simple right? It's so obvious but you would always overlook it. A lake that is able to hold all types of magical water creatures and even a giant squid, who is said to have resided in a lake near the Castle of Camelot. It is truly ancient in of itself.