Learn English – What does “cavernous room” mean or look like

To brace means "make (a structure) stronger or firmer with wood, iron, or other forms of support" (Webster's). So it means get ready to withstand some kind of extra stress. "Brace yourself" is a very common English expression.

'Faust' is the main character in German legend. From Wikipedia:

Faust or Faustus (Latin for "auspicious" or "lucky") is the protagonist of a classic German legend. Though a highly successful scholar, he is unsatisfied, and makes a deal with the devil, exchanging his soul for unlimited knowledge and worldly pleasures.

Making a 'Faustian bargain' can be interpreted as making a deal with the devil - it may seem like a good deal, but there is always a catch, and that catch is usually very, very bad.

Here is a wikipedia article discussing 'Deals with the Devil', which they also term as a 'Faustian bargain':

http://en.wikipedia.org/wiki/Deal_with_the_devil