I've been to lots (two DS, one about to go to Uni) and it was great fun but do wear comfy shoes!
It's best to view yourself as transport for the potential student and let them see exactly what they want to. Your other role is to encourage them to go up to tutors and ask questions about courses. There is lots of information that isn't written down.
One son says that they are "selling" themselves to you so you can ask what you want (politely of course). Don't focus on accomodation too much as it's usually a bit of a lottery as to what you get allocated.
Don't be bowled over by a vast and beautiful green campus in the sunshine. Imagine it in autumn or winter with the wind blowing and the rain lashing down. Students are not at Uni in the summer.
We saw quite a lot of Unis and I suggested DS1 and 2 made a list with their own categories allocating points out of ten for each.
E.G. course, location (distance from home, large town, city, suburb, remoteness), transport issues at Uni, atmosphere, facilities that are important to DS (e.g. sports - not so good in some London Unis), food (try out Uni cafe), clubs and societies available, reputation of Uni and course in various league tables, grades required etc.)
Have a great time.