Marvel: Ultimate Alliance/Bifrost Bridge

Before you start Valkyrie will ask you to find her Dragon Fang sword in this area which is optional. Anyway, you now encounter Viking soldiers coming out and attacking in this space-like area with the Viking ships floating in the air.

Light Up The Night
Around this area, you need to light up all the torches to open up another section where the gear is. On the way, make sure you match the stones up with the same symbol to cross to the next area where the gear is. Turn the gear with the superhero which has better strength to open up the Midgard gate.

Road to Wrecking Crew
The only thing you have to worry about through this narrow area is more Vikings and a drawbridge you need to lower it. The next narrow area is tricky. You have to dodge the fireballs the statues were blowing towards you until you reach the end where the SHEILD access point it.

Showdown with the Wrecking Crew
The Wrecking Crew is equally as tough as your team. However, if you want the balance tipping towards you, use the Extreme Power on any other of your team to cut their health to a limited extent. Melee and superpower them until the four is defeated. Then destroy the barrier blocking the gate.

Special note: If you choose Elektra, she'll have a different dialogue with one of the crew. Same with Luke Cage who also has it too.

Valhalla
Now you have access to Warrior's Hall in Valhalla. The only final sidequest is to talk to Weasel: Choose the first one about the final password into Black Widows laptop.
 * Talk to Dr Pym about Ivan.
 * Talk to Black Widow about Dr Ines.