Personally i would really reccomend going to as many uni open days as you can (within budget and available time, of course.) I was lucky enough that my parents supported my want to visit the open days, and we ended up going to about 15 in total, including a couple repeats of some to get a second look. I really found them useful, got a complete experience of everything, the vibe, the accom, the vibe of some of the lecteururs and my experiences completely changed my view on whether i wanted to go to some of the unis. UCAS fairs are also good, i went to one, however i did like certain stuff from what i saw at it about certain unis, but when i actually went to their open days i was less than enamoured. For example, i found that one uni i didnt like their teaching style when i found out more of how the course would be, which i didnt get from the website (despite thm having an overview of the course, it was something that i gained in person.) One uni really got me interested with a taster lecture, with a really engaging and interesting teacher. While another made me not want to go with a teacher that didnt enthuse me or get me interested in the subject, just made me... meh. Furthermore, while certain modules for one uni that i was particularly interested in were included on their website, speaking to the faculty at the open day and taster session allowed me to find out that the lecturer who specialised in that area and taught those was leaving, and wouldnt be replaced by someone with the same specialisation in the field, so what had drew me to that course wouldnt be available to me.
of course its slightly different for me as none of the unis were more than 4 hours away (theoretically, one had a maaasssive traffic jam on the way back which wasnt fun with a car without working aircon in a summer heatwave), we travelled by car instead of train and i ended up staying overnight at 2 of the unis i visited. for those that we stayed at, we tried to get the cheapest place possible, which as we had a car helped as we were able to go for the cheaper places out of the city a bit as we could drive in to the city the next morning. but i super reccomend seeing the places, they were really helpful and helped reduce the stress and fear of the process and unknown for me a whole bunch.