The pinnacle of the whole game are the 24 hours of Le Mans. You have to race in underpowered cars and rank up to get access to better cars. The smaller races are great but you are always looking at the main attraction. You can adjust the race time to your desires. I always did the 24 hours in 24 hours real time. You can only save the game when you are doing a pit stop. In addition you have to watch your tires and fuel level to make for the ideal pit stop. There are also weather changes which made the whole race and planning more challenging.
Unfortunately the game doesn't work with current OS' and it only lives in my memories. But I really want to relive the old times where I did the 24 hours in a couple of days, never had the possibility to do it in one stint.