Well, that's one of the places Wan would not want demolished - the ritual room specifically and anything connected to it that might still hold the darkness that tainted it - until it could be spiritually cleansed.

Also, he'd like to discuss with those who know about turtle health, what would be okay for 'filling in' the hollowed out parts of the shell that was done for the prison - not just sealing them up and making them inaccessible. Which would mean the small parts of the building that block off those entrances would need to remain as well.

Along with leaving the gardens as is, that's what Wan will be fighting for in regards to what should not be demolished on the palace grounds, but rather guarded until such time as they can be properly taken care of.

as an afterthought - is the portal to the Turtle's Head still around? If so, leaving access to that until it can be closed might be a good idea, too.