Once in a while, a prepositional phrase may act as a noun. This is fairly rare. A noun prepositional phrase generally acts as the subject of a sentence or as a subject complement.

In front of the class is a stressful place to be. (subject)
The most stressful place for me is in front of the class. (subject complement)

In these cases, there is usually a noun in front of the prepositional phrase that is implied or understood, but not written.

(The spot) in front of the class is a stressful place to be.
The most stressful place for me is (the spot) in front of the class.