Voted Best Answer
Nov 23, 2012 - 07:29 AM
I think the use of "a" can be complicated, but one rule you can hang your hat on is that forms of "ir" are almost always followed by "a" whether goint to a place (al estadio) or to do something (a comprar). There is no form of "ir" in your first sentence, so it is simply "es dificil viajar." Note also "I want to buy something" is "Quiero comprar algo", again no "a". But "I want to go home" is "Quiero ir a casa." (or "irme a casa" a form not covered by level 3).