Harry had never even imagined such a strange and splendid place. It was lit by thousands and thousands of candles that were floating in midair over four long tables, where the rest of the students were sitting. These tables were laid with glittering golden plates and goblets. At the top of the hall was another long table where the teachers were sitting. Professor McGonagall led the first years up here, so that they came to a halt in a line facing the other students, with the teachers behind them. The hundreds of faces staring at them looked like pale lanterns in the flickering candlelight. Dotted here and there among the students, the ghosts shone misty silver. Mainly to avoid all the staring eyes, Harry looked upward and saw a velvety black ceiling dotted with stars. He heard Hermione whisper, "Its bewitched to look like the sky outside. I read about it in Hogwarts: A History."
It was hard to believe there was a ceiling there at all, and that the Great Hall didn't simply open on to the heavens. (Harry Potter and the Sorcerer's Stone)
The phrase, at all, is not clear which meaning does it intensify: (1) hard to believe or (2) there was a ceiling there. Which one is it?