What happens when Nesta goes to the seventh level of the library?

Nesta is unnerved when she goes to the seventh level of the library. The darkness seems to rise and fall like it is breathing. She hears something calls her name. Then Gwyn arrives and gets her attention. Gwyn notices that Nesta is distraught, and she asks her what she sees. Nesta wonders if Gwyn sees things in the darkness. She says she does not, but some of the others do and say that the dark has trailed them to their doors. Nesta says that she saw pure darkness and thinks to herself it is like what she saw in the Cauldron. Gwyn tells her to go higher and not look back. She senses something watching. When they get to the fourth level, the presence seems to have disappeared.