The Elder Scrolls V: Skyrim - Dragonborn

From the Elder Scrolls wiki: To start the main questline, you must have at least started the quest The Horn of Jurgen Windcaller. If this quest is active or has been completed, the next time you visit a city in a major Skyrim hold (whether or not you have visited Solstheim before this point) two Cultists will stop the player and engage in a brief discussion, asking you whether you are the "Dragonborn" and then telling the player that the first dragonborn, Miraak, will soon be returning. They will then attempt to kill the player, and once they're dead, a note can be found on one of them, triggering a new objective for the player to visit Windhelm Docks.

They have to hold your hand and walk you through the content? This quest is practically automatic. Guys in masks literally walk up to you and throw fireballs in your face. If you bailed on the main quest so early you haven't even met the Greybeards, you may need to work a little harder on your focus.