Game Secrets:Sonic Adventure DX: Director's Cut
From Sonic Retro
Through hacking, a number of discoveries have been made about Sonic Adventure DX: Director's Cut.
There are a number of unused objects in the game. These objects include a button (Aoki Switch) in Lost World, tumbleweed in Windy Valley and a trash can in Speed Highway. Dude discovered these in the PC port of SADX. The tumbleweed in Windy Valley could be accessed by changing the graphic quality to the highest in the Settings screen during the autorun.
Casino Object oddity
If the player enters and exits the Casino area, incorrectly textured copies of the casino geometry will appear at their global location. This is sometimes used in theories that the Adventure Fields were all one map at some point, but in actuality this only happens because objects don't unload between areas in Adventure fields, and the Casino lights happen to be a very big and noticeable object.
Station Square Hotel Keys
flarn2006 discovered that if Big enters the Station Square hotel before clearing Ice Cap, the door to the pool area will be locked - something that never happens otherwise. Keys are found nearby - when placed in the appropriate sockets, the door will unlock. The hotel can be entered using a glitch involving Station Square's boat docks and a placeable object. A video can be found here.
Warning: If the player clears Emerald Coast early, they'll be sent to the Egg Carrier and become permanently stuck.
Mystic Ruins Door Unused Behavior
The door in the Mystic Ruins that Sonic, Knuckles and Gamma pass through to access the Master Emerald shrine and Red Mountain has an opening/closing animation as well as being fully textured on both sides. Unfortunately, through regular means it is impossible to view any of this in-game as the door is only seen from one side and never seen opening/closing to any of the characters.