If you've never been to the Indianapolis Motor Speedway, then you won't understand.
It's big. Big. Now, you can look up the Wikipedia article and read the facts about it – capacity of nearly half a million people, kilometer-long straightaways – but you won't really appreciate it until you're there.
I've seen a NASCAR race and an F1 race there, but this was my first 500. I was volunteering and working an early shift, so I didn't stay for the race itself. The souvenir tent was on the inside, so it was my first time inside the track.
It was cool to be there early and see the stands so empty on race day (yes, we get there really early to set up), but when we left at the end of our shifts, it was amazing to be inside the track while the race was running. (There are tunnels under the north and south ends of the track for access to the massive infield area.)
We were walking back to the parking lot (alas, no shuttles running during the race), and it was something to look around in all directions and see people seated off in the distance ... at times, the cars were far enough away that you really couldn't tell the race was going on if you didn't see the pylon or one of the big-screen TVs. (Think about it ... could you hear something more than half a mile away?) Then you'd see the cars flash by, practically at eye level, and gradually the sound would dissipate. All the way on the inside, people are moving to infield seating, walking around looking at the garage area, the souvenir stands, the Hall of Fame museum ...
Oh yes, and because you can bring your own beer (shocking!), most of them are happy, especially with the weather we had today. (Mid 70s, sunny. Perfect for viewing.)
I've been in Michigan Stadium before, but only once, when I was little. Since then, the largest field I've seen was probably the Silverdome, seating 80,000 at its finest. With five times that many people in that area, let's just say it was a good idea to leave early.
I do recommend that you go at least once, especially if you live anywhere nearby, just to say you've been. It isn't like the old days, where you'd have four solid weekends of fun and a massive party in the infield, but it's still amazing.