It’s actually “Night.” It’s the first episode where they encounter the Malon. There are peaceful aliens living in the darkness, but the Malon’s dumping of radioactive waste in their territory is killing them, so they attack Voyager thinking they’re like the others.

The Void is the one where they get trapped in a little pocket universe with some other ships and can’t figure out how to escape, while the pocket dimension is closing in on itself threatening to destroy everyone trapped inside.