@quest1on we were lucky enough to have gone to Cambridge back in February half term so got to walk round many colleges but not all thanks to the stupidity of extinction rebellion digging up Trinity lawn. 
We did look at the admissions statistics for his course and the colleges mainly because he didn't want to be 1 of 2 people taking his course as if you don't like that person you are stuck with them for 3 years so he chose ones that had 5 students or more. Some of the colleges want As in certain subjects so Queens wants As in maths, FM, physics and computer science so that means they would want Ds to get 4 A*s as he is taking all of those subjects so it ruled that out.
He has settled on a particular college but he is on the Cambridge HE+ scheme and was meant to be on a residential at that specific college which sadly got cancelled due to covid. They put on their own online open day for those students back in March. It included student's experiences from other colleges and a Q & A session.
I know Cambridge has an online open day 17th/18th September and it has good times ie 3pm so after school. Plus the colleges do their own too, you have to check to see when they are. It is completely shit that students are having to decide these things with very little personal experience. However much Ds wants this college though he has said I don't care if I end up in winter pool if they offer, I am taking it 