The crisis currently affecting Tamriel is far more vast than a single session can uncover. Your party can move on to the endgame of the campaign only after completing 2 game sessions, after which it will have earned enough success and experience to (hopefully) thwart a major threat to Tamriel.
Each province has its own endgame rules, which are described in its gazetteer. Endgame quests are different in several important ways. Each has a shorter day limit than a guild quest session, which is stated in its rules. Endgame quests represent a more intense session that presents the party with encounter after encounter. For this reason, endgame quests do not use overland movement for the party.