Marvel: Ultimate Alliance/Valhalla

After the cutscene with the villains, you now have your new missions from Nick Fury. You have to go to Bifrost Bridge to open the gateway between Earth and Asgard. The othe is to free the gods in Asgard.

Unfortunately you can't go to Warrior Halls until you complete one of the missions. Since there's very little to do, once you're done exploring, go through one of the places to start your next mission.