Here's why:
* It's not a playable area: The area behind that door is not part of the game's playable levels.
* It's a visual element: The door is part of the level design, meant to add atmosphere and intrigue, but it's not an actual entrance.
If you're looking for a specific objective or item in Mystic Ruins, you might be mistaken about its location or you might be thinking of a different game or level.
To make sure we're on the same page, please provide more context:
* What are you trying to do in the level?
* What platform are you playing on (Dreamcast, PC, etc.)?
* Can you describe the area near the ice door more specifically?
This will help me understand your question and provide a more helpful answer.