If it's tough in terms of the scale or effort required,

[Herculean][1]:
> 1. Of extraordinary difficulty, might, power, size, etc.; of or relating to Hercules in size or strength.
> 2. Requiring a huge amount of work, as a Herculean labour, a Herculean task. 


If it's tough in terms of its unsavouriness,

[odious][2]:
> 1. Arousing or meriting strong dislike, aversion, or intense displeasure.

You can find words similar to either sense by [using a thesaurus][3].


  [1]: http://en.wiktionary.org/wiki/Herculean
  [2]: http://en.wiktionary.org/wiki/odious
  [3]: http://thesaurus.com/browse/odious