He pushed into the interior, and Elizabeth followed him through the darkened narthex and into the
light beyond. She moved as if it hurt and kept her eyes down until the balcony passed above her head,
and the ceiling rose up. Beckett watched her face as she took in the rafters and the char and the
fixtures hung like iron crowns.
"took in" is another way of saying "looked at it" but it also has a contemplative feeling to it.
"I looked at the wall", doesn't invoke any feeling.
"I took in the painting on the wall", means not only did you see it but you thought about what you were seeing.
"I looked at the painting on the wall and took it in". This is another way of saying the same thing.
You "take something in" when you look at it and start to think, or you start to have an emotional reaction.
Elizabeth looked at, and "took in" the rafters and the char (char is that black burnt wood, or perhaps in this case it is wood that has been blackened by the smoke of candles over many centuries) and the fixtures hung like iron crowns. "Fixtures hung like iron crowns" is a simile, or a comparison between the actual object and some different object. The fixtures means chandeliers. He describes them as "iron crowns" so I imagine very old iron chandeliers which are hung from the ceiling with a chain, and on the chandelier are many candles. That looks a bit like an iron crown, don't you think? It's a very nice simile.