So I think that Devilry mentioned it already, but in the floating temple of the godess above Lakeview there is a room where the player can see there achievements, character sprites and so. In the corruption section right at the entrance of it there are two achievement crystal, one up and one down. The one bellow can't be access, because the floor tile that should be the entrance behaves like a wall and blocks the access.
Since it hasn't been pointed out clearly I just wanted to do so, since I don't know if it's a bug or if it was intended because the achievement wasn't implemented yet.
On that, have a nice day