How should castle doors be attached? I'm trying to plan the pieces I'll need for a castle door.
I know I need 2 of these doors.
Based on the part list for Adventurers Tomb set, it looks like I'll need several shutter holders, right?  Is there a way to fill in the curves around the top so the front is solid?
The Adventures Tomb 2996 set you mentioned uses shutter holders to mount the door and a 1x6x1 arch to cover the space behind the doors:





It is also very common to use a 1x6x2 arch, as was done in Dark Fortress Landing 8802:



As I mentioned in another answer, these clips generally attach to the back of the door, not the side. The geometry is more complicated to completely fill if you want to have the doors hinge from the side.