The Shattering of Our World
Although the expansion is a few weeks yet, the great cataclysm that is tomorrow. Our world will be forever changed, so now is your last chance to visit those places of nostalgia, finish those epic quest chains and say goodbye to all the things that are going away.
As an additional reminder, make sure you log out in the old world if you’re not a mage or engineer, since the portals in Dalaran and Shattrath are going away and it’ll be a long trip home otherwise.