After I've beaten the Rift Guardian and grab the loot, I teleport back to town and talk to Orek to get the gold and experience. Then, there's a countdown for about 30 seconds while the rift portal stays open. I go through the portal again, but I find that I'm at the entrance of the rift, with the enemies cleared out, naturally. Then I run around a few seconds before I'm taken back to town again.
Why does the rift stay open? What am I supposed to do?