The battlefields are randomly generated... so unfortunately no walk throughs.... (not for inside the dungeons in anycase...)
As for the locked entrances...
Like the battlefield key you found in the main game, there will be more of those.... each one unlocking an entrance.
There are 3 in act 1
6 in act 2-4.
You can find a walkthrough for the game itself though, and it will have the locations of all the battlefield keys. The official Strategy guide
Hope this helps...
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