Opendays.com has a calendar of all the open days, still lots left this term if anyone is inspired!
As said, DD is doing it different to DS. She is pretty certain she wants Ancient History so I have suggested she starts looking at courses and locations.
DS found by looking at a couple early on he knew what kind of location he wanted, then he drew up a list of possibilities. I think he visited 7 in total, though Oxford and Cambridge were with school.
I went on one, and on that one we did a thorough exploration of accommodation so he had a good idea of what it was about. DH took him to others, but kept in the background.
Most of DSs uni choices interviewed (MPhys) but it was kind of an offer holders day too, he spent the day there, had lunch with students, did a sample lecture. One, I think it was York, ran a parents programme but DH declined.
Personal Statement is a huge stress, get it started over the summer!
Don't forget Uniq/Sutton Trust applications for summer school next summer. Think Uniq was January.