Emptiness

Two spacecraft fly with the galaxy on one side and intergalactic space on the other.

"Ahead and behind, the walls of the Rift shimmered, a haze of stars too far away to resolve into individual points of light. The walls curved gently toward a starry floor, so many parsecs 'beneath' the granite keel of the city that it seemed to be hidden in a rising haze of star dust.
"'Above' there was nothing; a nothing as final as the slamming of a door. It was the empty ocean of space that washes between galaxies."
-James Blish, Earthman, Come Home, Chapter Three: The Rift IN Cities In Flight (London, 1981), pp. 285-297 AT pp. 285-286.

"A viewscreen showed us Landomar's sun, already dwindled, and the galaxy filling half the sky with clots and sprawls of glow. That was to starboard; the vector we wanted to build up ran almost parallel to the rim. Portward yawned emptiness, here and there the dim spindles of other stellar continents."
-Poul Anderson, World Without Stars (New York, 1966), Chapter III, p. 17.

Combining the two accounts, intergalactic space is an "ocean" and galaxies are "stellar continents." They used to be called "island universes." Blish writes "nothing" and "empty ocean" and Anderson writes "emptiness."

Blish adds the further concept of the Rift:

"The Rift was, in effect, a valley cut in the face of the galaxy. A few stars swam in it, light millennia apart -" (p. 286)

Thus, Anderson's characters visit a planetary system between galaxies whereas Blish's Okies find a system within the Rift. I think that Blish says somewhere that the mere random movements of the stars had opened up the Rift although he also suggested in conversation that he might have been thinking of the space between two spiral arms.