Other forms: mainlands
A mainland is the land covering a continent, as opposed to islands off its coast. When you take the ferry back after visiting Block Island, you can say you're "returning to the mainland."
The rocky coast of the mainland might make for a difficult landing in your rowboat — or you might enter a race that requires you to swim from the mainland to a tiny island and back. You could also refer to "mainland United States" to distinguish it from the island state of Hawaii, and its residents might even call you a mainlander when you vacation there.