We have been married for 24 years, love each other and actually like each other. He works out of town for weeks, even months at a time. We talk almost every day. Our 11 yr old son and I went to see him (about 700 miles away) about a month ago. During our visit we wanted to find something fun things to do in the area. One night I was on the computer looking for ideas and came across where he had been going to websites for dating, affairs, hookups, whatever you'd call them in the local area he was in. I'm not sure what to make of this. We have had friends that are divorced because this kind of thing and we always agreed it was wrong and stupid. It's not the kind of thing he would do. I want to think this was just him looking on the computer, but there are other websites on the computer for "looking". What should I do? I'm mad but mostly hurt.

He's either cheating or he isn't.
You are asking total strangers, knowing full well that we don't know any more than you do. So you are really asking, what should you say to him? Because knowing stories from others isn't going to mean a thing.
(I will say that my elderly father got on such sites after my mother died! Men!)

Anyway, the answer of course is to be brave and ask him point blank, looking him gently and calmly in the eyes, since the eyes rarely know how to lie. I'm guessing that you are afraid to ask because you are afraid that you might think he's lying... and that's almost worse than not asking. But ask you must.

If your relationship is truly as you described, he was probably just curious or imaging a situation he could fantasize over while he was alone and away from his family for a long time. If you ask him about it, he'll probably be quite embarrassed and not be sure how to tell you he needs to take care of his sexual desires while on the road.

If your relationship is not quite as you described, or perhaps is not what you perceive it to be, maybe he has been looking to cheat while he's been away.

You can sit and speculate like I am, or you can ask him. At least if you ask him, you can gauge his reaction.