There are .621 miles in one kilometer. So if you multiply .621 miles by 100, you get 62.1 miles. That means that a 100 km race will cover 62.1 miles. That is a lot of miles! To successfully run such a long race, you will need to carve out months of time to train, learn about endurance running nutrition and how your body responds to certain foods, and how to properly recover in between runs to keep your body injury free.
Ultra running is certainly not for the faint of heart. Running tens of miles at a time (even one hundred miles or more in some races) certainly takes a toll on the body and the mind. Mentally, it is tough to get through a race like - especially if there are inclement weather conditions and personal struggles you are dealing with. And then pushing yourself through the training and preparation that it takes to get yourself ready for an ultra race is another challenge. It typically means very long, strenuous runs and workouts. Sometimes it even means figuring out your schedule to accommodate for multiple workouts in a day. And then when you are not working out, running, or putting yourself through intense physical endurance and pushing those limits, you have to be on top of your nutrition and hydration, making sure you are eating often and enough at each meal, but sticking to balanced and nutritionally well rounded meals and plenty of water. And then there are the long list of things that you have to GIVE UP to accomplish your ultra dreams. When that alarm goes off for your early morning run, that means hours of sleep lost, birthdays and parties that you skip out on to go to sleep, office donuts and after work happy hours with co-workers, etc.
I certainly do not say all that to scare you off, because running a race that distance is the ultimate test of will for runners, and can provide such great pride and motivation for your running career! Plus, you set a fantastic example of determination, work ethic, and dedication to those family and friends around you who see you giving so much of yourself to accomplish your goal!