I had to do jury service a couple of years ago, at the Old Bailey so no parking issues as I had to suffer rush hour commute on the trains and it was boiling at the time. First couple of days were much as you described, lots of waiting around, but no chance of fresh air as once you're in you're in for the day apart from lunch.
Finally got picked for a case, 16 year old kid stabbed and killed by a 17 year old (lovely).
The scary thing was most of the jurors seemed to have taken a wrong turn on the way to Jeremy Kyle's studio. We had 9 days of forensic evidence, witness statements, cctv to get through then retired to consider our verdict.
This took 2 days as most of the jury appeared to have not listened to previous 9 days of blurb, and it had to be explained again.
Some of the jury were so easily swayed one way or the other, like the guy in the Fast Show who can never make his mind up.
Murder verdict arrived at eventually, and at least 18 years for the perp. The most depressing 3 weeks in summer I've ever had, sordid and nasty stuff. I had been passed over for the case before this one, which was a double, drug dealer murder which went on for 6 weeks so could have been worse.
Really hope I never get picked again or have to be judged by my "peers".