Each of the Door is labeled and marked with a picture of whatever is inside it. At least you assumed based on the design. For example,

The first one, had a symbol of a blue slime creature, below it is a word, unknown to you. A language from this world apparently. You wonder if the books are written like this...

In any case, several doors stretched far to the ends of this hallway seems available to explore inside, all you have to do is be ready to encounter whatever's behind it.