Lake of Mirrors is a CTM map that is both super hostile and hardcore. In fact, this map all but self destructs upon loading, that’s how good it is. Don’t let the pretty scenery and small monument fool you (you only have to collect four items to complete the monument). Every single one of those items will push you to the very limits of sanity – and perhaps even to the very limits of life. Be very careful though, this map is entirely unyeilding. You die and it is back to the saves folder to re-extract the .rar and try yet again.
Description taken from: https://minecraftworld.wordpress.com/2013/04/29/lake-of-mirrors-hardcore-minecraft-hostile-ctm-map/