If you look closely, you can see some weirdness with the angle of the stairs at the back of the scene. I tried to replicate that in the tile with an angled staircase. Once I started drawing the map, I decided that the dragon's lair might have been in a former temple (the slightly raised opening in the back behind the column led me to put a shrine/altar in the corner).
BORDER UPDATE: The border tiles that I posted on Tuesday have been updated with darker walls. More borders and corners will be coming shortly.