The Lake of Origin is found deep in the Everfree Forest.
The lake has a strange way of working. When you look in, you see you from the most miserable part of your life. Pinkie Pie saw herself when her mane and tail deflated, but the reflection is not miserable, it wants to make you miserable. It is often foulmouthed and has a short temper. The lake can remember encounters, Vinyl Scratch asked her reflection where Pinkie Pie went when she went missing, and the lake answered correctly.
The lake can be used for interrigation, and when Montana Ulan was in it, he brought Surprise back to life after she died.