The floors where the same the ones he'd walked up and down them for days at a time.
It was him who'd been changed, for better of for worse and it was him who felt out of place inside the Vatican walls even though he had prayed to be in there safety when he'd been in Transylvania.

Many things may change a man – fear, loathing, lust or just the possibility of something untouchable and unquenchable.
Carl had been changed by fear and by lust, strong emotions that at times had felt as palatable to him as food and drink, and by sorrow so overwhelming he'd thought he'd drown under the sway of it.
But he had been pulled up from the sea of sorrow and sent back to dry land and safety by the greatest of his friends Van Helsing, whom had left to pursue his own daemons leaving Carl to battle his own walled up behind tradition and vows that had meant everything and now were as worthless as grains of sand.

Van Helsing came back, fresh blood on his hands and his soul from the latest fallen man and Carl tried his best to wash away the invisible stains that wouldn't leave his friend; that would damn him to hell.
"So I am damned" Van Helsing had said shrugging his shoulders as if it didn't matter and continuing with life but Carl had become obsessed with this new crusade – to rid his friend of sin and in someway repent both of them.
Holy water, rosaries, prayer, anything he thought might cleanse away the degradation of years, nay, centuries of death and blood until it was all he though of day and night.

A touch to his shoulder one night broke him out of his belief and a kiss brought him out of his fixation until he was falling, sinning in a way he had forbid himself for so long and being changed again, changed in a way he could never return from.
This change he did not fight and did not regret, with his legs locked about Van Helsing as the other man moved within him capturing Carl's soul for his own and promising him the world in return.

This change might bring him the worst of all retributions but it was a change he welcomed, that washed away the uncertainty for Carl had fallen in love.